Reentrant Phenomena Research Articles

Re-entrance and localization phenomena in disordered Fibonacci chains

We consider quasiperiodic tight-binding models and the effects of disorder on wavefunctions in one dimension. While in an infinite system all states are localized by disorder, however weak, in finite chains the situation is more interesting. It was shown recently for the Fibonacci nearest neighbor hopping model that certain states can be delocalized for weak disorder: Their inverse participation ratios (IPRs) decreases with disorder strength at weak disorder, goes through a minimum, and thereafter increases for stronger values of disorder. Finite size scaling analysis shows the existence of different classes of wavefunctions and non-monotonic (re-entrant) behavior. The scaling variable depends on a new critical exponent ν whose value is determined by the parameters of the quasiperiodic Hamiltonian. We show that this re-entrant dependence of the IPRs exists for the general class of Fibonacci models and provide the explanation for the different behaviors observed in terms of the type of spatial characteristics of the wavefunctions.

Magnetism in two antiferromagnetic Ising nanoparticles under an applied transverse field

The phase diagrams and magnetization curves of two antiferromagnetic Ising nanoparticles (A and B) under an applied transverse field are investigated by using the effective-field theory with correlations. The nanoparticle B is a size larger than that of nanoparticle A. The effects of size on the magnetic properties are discussed. Some characteristic features, such as the reentrant phenomena, are found in these properties of both systems, when a finite transverse field h is applied. The nanoparticle B exhibits the ferrimagnetic behaviors, such as a compensation point.

Landau-Ginzburg-Devonshire Theory of the Grain Size Effect on the Ferroelectricity in BaTiO <sub>3</sub> Nanoceramics

The grain size effect on the ferroelectric phase transitions and dielectric properties of BaTiO3 nanoceramics is described by higher order Landau-Ginzburg-Devonshire theory. A structurally stable 8th-order Landau-Ginzburg-Devonshire potential with the 2nd- and 4th-order coefficients varying with temperature and grain size is proposed for a phenomenology of BaTiO3 nanoceramics. The temperature-grain size phase diagram constructed on the basis of this potential model describes well experimentally observed cubic-tetragonal-orthorhombic and cubic-orthorhombic-rhombohedral triple points, and ferroelectric to paraelectric to ferroelectric reentrance phenomenon. The spontaneous polarization and dielectric constant of BaTiO3 nanoceramics are calculated. It is shown that dielectric anomalies appear at the phase transitions and dielectric peaks are depressed and diffused with decreasing grain size.

Effects of a random single-ion anisotropy on the spin-[formula omitted] Blume-Capel (BC) Ising model

The magnetic properties of the spin-5/2 Blume-Capel model are investigated by means of the Mean-Field theory in a random single-ion anisotropy environment. The T=0 phase diagram is singled out as well as the thermal behaviors of the lattice magnetization. Numerical results reveal beyond first- and second-order phase transitions, the existence of isolated critical points. Novel magnetic orders are detected in the low-temperature range. Some thermal phase diagrams are constructed where the reentrant phenomenon often emerges. Interesting hysteresis loops are got when an external magnetic field constraint is imposed on the system.

Thermal and Optical Characterization of Multiple Hydrogen Bonded Liquid Crystals and Its Application in Display Devices

Novel homologous series of phloroglucinol (PG) and 4-n-alkyloxybenzoic acid (nOBA, n = 4 to 12) hydrogen bonded liquid crystal (HBLC) complex have been designed and synthesized. In the self-assembly process, intermolecular interaction between the molecules produce the multiple HBLCs with various shapes and structure. Existences of multiple hydrogen bonds in the PG+nOBA HBLC complex are confirmed by FT-IR spectroscopic method. Textural changes along with that phase transition temperature are identified by polarizing optical microscope (POM). Due to the polymerization, an induced stabilized smectic phase along with re-entrant disordered phase is noticed in the present PG+nOBA HBLC complex. The thermodynamic properties such as enthalpy values, thermal stability and thermal span width are analyzed by differential scanning calorimetry (DSC). An induced re-entrant phenomenon in the present HBLC complex is due to the dipolar aggregation has been discussed. The band gap energy is calculated by UV–Visible spectrometer (UV–Vis) which gives the clear evidence for the existence of band gap energy value (Eg = 3.5 eV) in the present HBLC complex. The desirable band gap in the present HBLC and its display device application is reported in the present communication. The other liquid crystal parameters (thermal stability, tilt angle, etc.) are also discussed.

Magnetism in an antiferromagnetic Ising nanoribbon

The phase diagrams and magnetizations of an antiferromagnetic Ising nanoribbon are investigated by using the effective-field theory with correlations. The numerical results show that the magnetic properties in the nanoribbon may exhibit some different behaviors, depending on whether the applied transverse field takes zero value or a finite value. In particular, the reentrant phenomena and the ferrimagnetic behaviors have been found in the both cases, while some differences are observed. It has been discussed that the sign reversal of magnetization is possible, when a transverse field is applied to the system.

P1602Basic electrophysiological modifications induced by carvedilol in unstrectched and stretched ventricular myocardium

Abstract Background Acute regional ventricular stretch (ARVS) is a pathophysiologic event that may occur in certain situations, originating arrhythmogenic effects through the mechanoelectrical feedback. Mechanical effects of stretch originate calcium-related changes as sarcoplasmic recticulum Ca2+ overload that can trigger Ca2+ diastolic leaks (store-overload-induced Ca2+ release, SOICR), mediated by the cardiac ryanodine receptor (RyR2). SOICR seems to be implicated in the mechanisms underlying stretch-induced arrhythmias. Carvedilol can inhibit the overload of Ca2+ through blocking of beta-adrenergic receptors, and also suppress the release of Ca2+ induced by the SOICR. Purpose The aim of this investigation was to study the effects of carvedilol on the changes in ventricular refractoriness produced by AVRS, directly related with reentrant phenomenon and life-threatening arrhythmias. Methods Eleven adult male New Zealand White rabbits (3–3.5 kg) were heparinized (2500 IU) and euthanized by intravenous injection of sodium thiopental (100 mg/kg), according to European Ethic Guidelines. The hearts were excised, isolated and perfused in a Langendorff system. A pacing electrode and a recording multielectrode (121 electrodes) were placed on the left ventricle epicardium. The ARVS was produced by an “ad hoc” device introduced into the left ventricle. The ventricular effective and functional refractory periods (VERP, VFRP) were determined by the ventricular extrastimulus test with a basic cycle length of 250 ms, previously and at the third minute of ARVS, in control conditions and under Carvedilol (1 μM) infusion. The pacing threshold was determined for each situation and the stimulus amplitude was twice the diastolic threshold. A Student's t-test was used. Significance was reached when p<0.05. Results Myocardial stretch reduced VERP and VFRP with respect to pre-stretch values under control conditions (VERP: 110±13 vs 99±16 ms, VFRP: 119±13 vs 113±13 ms, p<0.05; n=10). No stretch-induced modifications of refractoriness were observed under carvedilol action (VERP: 139±18 vs 140±17 ms, VFRP: 161±29 vs 157±15 ms, ns; n=8). Before stretching, there were differences between control and carvedilol conditions (VERP: 110±13 vs 139±18 ms, VFRP: 119±13 vs 161±29 ms, p<0.001), and during stretch VERP and VFRP were significantly higher under carvedilol perfusion than in control conditions (VERP: 99±16 vs 140±17 ms, VFRP: 113±13 vs 157±15 ms, p<0.001). Conclusion The beta-adrenergic blocker and ryanodine receptor antagonist, carvedilol, attenuates the intrinsic electrophysiological modifications on refractoriness produced by myocardial acute local stretch.

Reentrant phenomena of a mixed spin (5/2,3/2) Isotropic Blume–Emery–Griffiths model (BEG) on a graphene layer

Abstract Magnetic properties of a mixed spins (5/2,3/2) Isotropic Blume–Emery–Griffiths model (BEG) on a graphene layer have been studied within the framework of the Monte Carlo simulation. We have investigated the effects of the next nearest neighbors exchange interaction, the biquadratic exchange interaction and the longitudinal magnetic field on the critical and magnetic behaviors of the system. Interesting phenomena have been remarked. In particular, for appropriate parameters of the Hamiltonian, the system exhibits magnetization plateaus, double reentrant phenomena and compensation behavior.

Magnetism in an antiferromagnetic Ising nanoparticle under an applied transverse field

The phase diagrams and magnetizations of two antiferromagnetic Ising nanoparticles (A and B) under an applied transverse field are investigated by using the effective-field theory with correlations. The nanoparticle B is a size larger than that of nanoparticle A. Both nanoparticles exhibit the reentrant phenomena. The numerical results show that the magnetic properties in the nanoparticle may exhibit rather different behaviors, depending on the size of a nanoparticle.

Devlin-like approach to a spin-1 transverse XY model with biquadratic exchange and single-ion anisotropy

The effect of the biquadratic exchange interaction on the phase diagram of a d-dimensional spin-1 transverse XY model with easy-axis single-ion anisotropy is studied by employing the Devlin-like two-time Green functions framework. The chain of equations of motion is closed adopting the random phase approximation for the exchange higher order Green functions and treating exactly the crystal-field anisotropy terms. For short-range interactions and d > 2, analytical estimates and numerical calculations predict a reentrant behavior of the critical lines close to the magnetic-field-induced quantum critical point for appropriate values of the single-ion anisotropy parameter and suitable combinations of the bilinear and biquadratic exchange couplings. Remarkably, increasing the biquadratic exchange reduces or destroies the reentrant character of the quantum critical lines, in qualitative agreement with the findings of the Anderson-Callen-like strategy. In our formalism, the easy-plane anisotropy case can be studied similarly but the phase diagram and the quantum critical scenario do not present any reentrant phenomena.

Magnetism in an antiferromagnetic Ising nano-ladder under an applied transverse field

ABSTRACTThe phase diagram and magnetization curves of an antiferromagnetic Ising nano-ladder in an applied transverse field are investigated by using the effective-field theory with correlations. They are compared with those in the antiferromagnetic Ising ladder (or bulk). Some characteristic features, such as the reentrant phenomena, are found in these properties, when a finite transverse field h is applied or even when h = 0.0.

Impurity-induced Shiba bound state in the BCS–BEC crossover regime of two-dimensional Fermi superfluid**Project supported by the National Key R&D Program of China (Grant No. 2017YFA0206302).

For a two-dimensional ultra-cold Fermi superfluid with an effective static magnetic impurity, we theoretically investigated the variation of the Yu–Shiba–Rusinov (YSR) bound state in the Bardeen–Cooper–Schrieffer (BCS) to Bose–Einstein condensation (BEC) crossover regime. Within the framework of mean-field theory, analytical results of the YSR bound state energy were obtained as a function of the interaction parameters. First, when the background Fermi superfluid system stays in the weakly interacting BCS regime, we found that the YSR bound state energy is linearly dependent on the gap parameter with its coefficient slightly different from previous results. Second, we discovered re-entrance phenomena for the YSR state and an upper bound of the strength of the interaction between the paired atoms. By carefully analyzing the bound state energy as a function of the interaction parameters, we obtained a phase diagram showing the existence of the YSR state. Finally, we concluded that the re-entrance phenomena and the critical point can be easily experimentally detected through measurement of radio-frequency spectroscopy and density of states using current experimental techniques.

Study on Re-entrant Jet Pressure Characteristics of Ventilated Cavitating Vehicles

When the re-entrant jet phenomenon generation at the end of ventilated cavity, body surface form high pressure under the meanflow impact. This high pressure moves downstream with the development of ventilated cavitation, and will arouses significant effect on the motion stability of the body. Based on this, this paper through the experimental observation of the reentrant jet phenomenon, captures the characteristics of the pressure surface, the dynamic changes of the re-entrant jet pressure of the underwater vehicle during the development of the cavity are studied. The relationship between the velocity of the cavity and the characteristics of the re-entrant jet pressure is obtained, and under the condition of the vehicle at the angle of water shot back pressure feature. The results show that the re-entrant jet pressure is much higher than the pressure inside the cavity, and the re-entrant jet pressure is obviously changed with the development of the cavities. There are differences in the pressure characteristics between the surface and the back surface.

Unique magnetism in a graphene ladder-type Ising system under an applied transverse field

The phase diagrams and magnetization curves of a graphene ladder-type Ising system under an applied transverse field are investigated by using the effective-field theory with correlations. They have exhibited many characteristic phenomena, such as the reentrant phenomena exhibiting the three transition temperatures. In particular, the thermal variations of transverse magnetizations have exhibited some characteristic features not found in other transverse Ising models.

Reentrant Phenomena in an Antiferromagnetic Ising Nanoparticle and a Ladder-Type Ising System under an Applied Transverse Field

The phase diagrams and magnetization curves of antiferromagnetic nanoparticle and ladder-type system are investigated by using the effective-field theory with correlations. They have exhibited some characteristic features, such as the reentrant phenomena, when a finite transverse field h is applied and even when h = 0.0.

Delay-induced transitions in the birhythmic biological model under joint noise sources

In this paper, the combined effects of delayed feedbacks and noise on the enzyme–substrate reaction in the brain are examined. By means of the approximate methods, we analyze the stationary probability density function of the amplitude and the joint of displacement and velocity, finding that stochastic bifurcations can be induced by noise correlation and time delay. In Particular, the system undergoes a succession of two transitions as time delay is varied monotonically, namely, the reentrance phenomenon appears. The analytical results appear to be in reasonable agreement with the direct numerical simulations of the original system. From the biological point of view, the reaction rate of the enzymatic substrate reaction can be enhanced or diminished by Gaussian colored noise. More intriguingly, an increase in displacement feedback will retard the reaction rate, nevertheless, whether an increasing velocity feedback will benefit the reaction rate depends on time delay. It is worth noting that the chemical oscillations can be controlled to a low level when the appropriate time delay is chosen.

Quantifying Mg2+ Binding to ssDNA Oligomers: A Self-Consistent Field Theory Study at Varying Ionic Strengths and Grafting Densities.

The performance of aptamer-based biosensors is crucially impacted by their interactions with physiological metal ions, which can alter their structures and chemical properties. Therefore, elucidating the nature of these interactions carries the utmost importance in the robust design of highly efficient biosensors. We investigated Mg binding to varying sequences of polymers to capture the effects of ionic strength and grafting density on ion binding and molecular reorganization of the polymer layer. The polymers are modeled as ssDNA aptamers using a self-consistent field theory, which accounts for non-covalent ion binding by integrating experimentally-derived binding constants. Our model captures the typical polyelectrolyte behavior of chain collapse with increased ionic strength for the ssDNA chains at low grafting density and exhibits the well-known re-entrant phenomena of stretched chains with increased ionic strength at high grafting density. The binding results suggest that electrostatic attraction between the monomers and Mg plays the dominant role in defining the ion cloud around the ssDNA chains and generates a nearly-uniform ion distribution along the chains containing varying monomer sequences. These findings are in qualitative agreement with recent experimental results for Mg binding to surface-bound ssDNA.

Unique phenomena induced by an exchange interaction between two graphene-like Ising nanoparticles in an applied transverse field

The phase diagrams and the magnetizations of graphene-like nanoparticles which are constructed from two paramagnetic honeycomb units and an inter-unit exchange interaction r are investigated by using the effective-field theory with correlations. They have exhibited some characteristic phenomena, such as the reentrant phenomena, when the value of r is larger than r = 1.0 and a transverse field is applied.

Magnetism in a graphene-like Ising nanoparticle under an applied transverse field

The phase diagram and magnetization curves of two antiferromagnetic and ferromagnetic hexagonal Ising nano-particles with a next-next-nearest-neighbor exchange interaction which comes from the super-exchange interaction via a central nonmagnetic atom are investigated by using the effective-field theory with correlations. They have exhibited some characteristic features, such as the reentrant phenomena, when a finite transverse field is applied.

Nanophase Segregation of Nanostructures: Induction of Smectic A and Re-Entrance in a Carbon Nanotube/Nematic Liquid Crystal Composite.

Although representing drastically different chemical natures and types of interactions, the similarity of shape anisotropy of the constituents has created much interest in composites of calamitic liquid crystals (LCs) and carbon nanotubes (CNTs). Despite significant volume of studies on the physical properties of such composites, influence of CNTs on the celebrated re-entrant phenomenon in LCs has not been studied. We report here that a small concentration of CNTs doped to a "nematic mesophase-only" material not only induces the layered smectic A mesophase but also leads to the nematic-smectic-nematic re-entrant sequence as well, demonstrating the delicate interplay between the two entities. To explain this unusual observation, we propose nanophase segregation of the CNT as a possible mechanism. A combination of Flory-Huggins theory and Landau-de Gennes theory has also been provided supporting the observed feature.