Anomalous Memory Effects Research Articles

Influence of local defects in the generation of memory effect in Dy2Ti2O7 compound: Fe-doped study

The study of defect-induced effects in functional materials is high-priority research for the miniaturization of smart devices. To elucidate the influence of local defects stemming from intrinsic or extrinsic factors on the enigmatic behavior of cooperative spin dynamics, we investigated the Dy2-xFexTi2O7 compound within a narrow Fe substitution range (x = 0–0.15). Our experimental findings unequivocally demonstrate that the dynamic response of cooperative spins and the emergence of anomalous memory effect are intricately linked to local defects. Depending on the nature and dynamics of these defects, the dynamic response of cooperative spins undergoes alteration. Notably, observed anomalous effect becomes more pronounced in scenarios characterized by slower defect dynamics and when cooperative spins are further from equilibrium. The emergence and sensitivity of thermomagnetic hysteresis (memory effect) to cooperative spin dynamics and external stimuli underscore the richness of Dy2Ti2O7 as a material for captivating physics investigations.

Depressurization-induced changes in memory effect of hydrate reformation correlated with sediment morphology

Research on the memory effect can improve the rate and efficiency of hydrate reformation, which has important applications in gas hydrate technology. Depressurization is the most widely used gas hydrate dissociation method; however, studies on the mechanism of depressurization on memory effect are still lacking. In this study, the memory effects were compared and analyzed after the hydrate sediment was subjected to different dissociation patterns. The different dissociation patterns included depressurization (different backpressures: 4.5, 3.5, 2.5, 1.5, and 0.1 MPa) and single thermal stimulation dissociation pattern (STSP). The effect of depressurization-induced sediment morphology changes on hydrate-memory effect and gas conversion was obtained under different backpressures. The results indicated that the memory effect tended to remain stable in the STSP, but changed with depressurization dissociation. The memory effect after depressurization dissociation gradually weakened with decreasing backpressure. Notably, an anomalous memory effects was observed, wherein the memory effect was not weakened, but significantly enhanced after depressurization dissociation at 0.1 MPa. Furthermore, depressurization may not only change the memory effect but could also increase the stable interval of the memory effect and the supercooling degree. The average gas conversion ratio of stable interval after dissociation at 0.1 MPa decreased by nearly 8%.

Gas-Liquid-Solid Migration Characteristics of Gas Hydrate Sediments in Depressurization Combined with Thermal Stimulation Dissociation.

The exploitation of natural gas hydrate is always hindered by the migration of water and sands due to gas production. Depressurization combined with thermal stimulation is an effective method for hydrate dissociation. This paper reported the influence of gas–liquid–solid migration on morphological change of hydrate sediments in natural gas production using visualization method. Different backpressures combined with thermal stimulation methods were applied to simulate natural gas hydrate exploitation. Pressure compensation was first employed to study sediment recovery features. The expansion rate of a porous medium layer under combined dissociation and different backpressure (4.5, 3.5, 2.5, 1.5, and 0.1 MPa) was discussed. A 176% hydrate sediment expansion rate was found after the combined dissociation at 0.1 MPa. In addition, it was observed that the height of the water layer above the porous media after pressure compensation was gradually reduced with a decrease in backpressure and eventually disappeared at 0.1 MPa. It was also found that the disappearing water layer caused an anomalous memory effect phenomenon. Expansion and subsidence of sediments provide a better reference for hydrate exploitation and geological safety.

Influence of a Nitrogen Admixture on the Anomalous Memory Effect in the Breakdown of Low-Pressure Argon in a Long Discharge Tube

The memory effect (the dependence of the dynamic breakdown voltage U b on the time interval τ between voltage pulses) in pulse-periodic discharges in pure argon and the Ar + 1%N2 mixture was studied experimentally. The discharge was ignited in a 2.8-cm-diameter tube with an interelectrode distance of 75 cm. The measurements were performed at gas pressures of P = 1, 2, and 5 Torr and discharge currents in a steady stage of the discharge of I = 20 and 56 mA. Breakdown was produced by applying positive-polarity voltage pulses, the time interval between pulses being in the range of τ = 0.5–40 ms. In this range of τ values, a local maximum (the anomalous memory effect) was observed in the dependence U b (τ). It is shown that addition of nitrogen to argon substantially narrows the range of τ values at which this effect takes place. To analyze the measurement results, the plasma parameters in a steady-state discharge (in both pure argon and the Ar + 1%N2 mixture) and its afterglow were calculated for the given experimental conditions. Analysis of the experimental data shows that the influence of the nitrogen admixture on the shape of the dependence U b (τ) is, to a large extent, caused by the change in the decay rate of the argon afterglow plasma in the presence of a nitrogen admixture.

The anomalous memory effect related to the relaxation of surface and core moments observed in well-dispersed CoFe2O4 nanoparticles

Abstract Well-dispersed uniform cobalt ferrite nanoparticles were synthesized by thermal decomposition of a metal–organic salt in organic solvent with a high boiling point, and characterized by XRD, TEM and detailed magnetic measurements. The moments of CoFe 2 O 4 nanoparticles consist of the core and canted surface moments below 200 K, and the exchange-coupling between the surface and core spins enhanced the remanence ( M r ) to saturation ( M s ) magnetization ratio ( M r / M s ) at the temperature of 10 K. Interestingly, the anomalous memory effect was observed in a broad temperature range which can be attributed to the relaxation of surface spins below 200 K and the one from the moments of magnetically ordered entity larger than one particle above 200 K.

Anomalous memory effect in the breakdown of low-pressure argon in a long discharge tube

The characteristics of breakdown of argon in a long tube (with a gap length of 75 cm and diameter of 2.8 cm) at pressures of 1 and 5 Torr and stationary discharge currents of 5–40 mA were studied experimentally. The breakdown was initiated by paired positive voltage pulses with a rise rate of ~108–109 V/s and duration of ~1–10 ms. The time interval between pairs was varied in the range of Т ~ 0.1–1 s, and that between pulses in a pair was varied from τ = 0.4 ms to ≈Т/2. The aim of this work was to detect and study the so-called “anomalous memory effect” earlier observed in breakdown in nitrogen. The effect consists in the dynamic breakdown voltage in the second pulse in a pair being higher than in the first pulse (in contrast to the “normal” memory effect, in which the relation between the breakdown voltages is opposite). It is found that this effect is observed when the time interval between pairs of pulses is such that the first pulse in a pair is in the range of the normal memory effect of the preceding pair (under the given conditions, Т ≈ 0.1–0.4 s). In this case, at τ ~ 10 ms, the breakdown voltage of the second pulse is higher than the reduced breakdown voltage of the first pulse. Optical observations of the ionization wave preceding breakdown in a long tube show that, in the range of the anomalous memory effect and at smaller values of τ, no ionization wave is detected before breakdown in the second pulse. A qualitative interpretation of the experimental results is given.

Multiferroic nanoregions and a memory effect in cupric oxide

We report the observation of multiferroic nanoregions in cupric oxide, CuO, by means of resonant soft x-ray magnetic scattering. There exists an anomalous memory effect for the direction of the electric polarization in the commensurate-incommensurate magnetic transition that coincides with the ferroelectric transition. Scattering results, incorporated with simulations of diffuse scattering, lead us to propose a scenario that preserved spin handedness in the multiferroic nanoregions is responsible for this memory effect in the magnetically induced ferroelectric properties of CuO.

Anomalous memory effects on transport of inertial particles in turbulent jets

The letter focuses on a new phenomenology found in the far field of turbulent-free jets, where small inertial particles exhibit a local concentration peak on the axis. This finding contrasts with the prediction of classical models based on turbulent kinetic energy gradient transport assumptions, whereby particles should move away from the local kinetic energy maxima. This behavior is universal, i.e., it occurs no matter the details of the specific jet, and takes place irrespective of the inertia of the particles. As anomalous signature of the near field dynamics, it cannot be predicted on purely dimensional grounds. A new form of similarity allows to collapse the local particle flux profile on a universal curve.

Non-Markovian effects on the two-dimensional magnetotransport: Low-field anomaly in magnetoresistance

We discuss classical magnetotransport in a two-dimensional system with strong scatterers. Even in the limit of very low field, when ${\ensuremath{\omega}}_{c}\ensuremath{\tau}⪡1$ (${\ensuremath{\omega}}_{c}$ is the cyclotron frequency, $\ensuremath{\tau}$ is the scattering time) such a system demonstrates strong negative magnetoresistance caused by non-Markovian memory effects. A regular method for the calculation of non-Markovian corrections to the Drude conductivity is presented. A quantitative theory of the recently discovered anomalous low-field magnetoresistance is developed for the system of two-dimensional electrons scattered by hard disks of radius $a$, randomly distributed with concentration $n$. For small magnetic fields the magentoresistance is found to be parabolic and inversely proportional to the gas parameter, $\ensuremath{\delta}{\ensuremath{\rho}}_{xx}∕\ensuremath{\rho}\ensuremath{\sim}\ensuremath{-}{({\ensuremath{\omega}}_{c}\ensuremath{\tau})}^{2}∕n{a}^{2}$. In some interval of magnetic fields the magnetoresistance is shown to be linear $\ensuremath{\delta}{\ensuremath{\rho}}_{xx}∕\ensuremath{\rho}\ensuremath{\sim}\ensuremath{-}{\ensuremath{\omega}}_{c}\ensuremath{\tau}$ in a good agreement with the experiment and numerical simulations. Magnetoresistance saturates for ${\ensuremath{\omega}}_{c}\ensuremath{\tau}⪢n{a}^{2}$, when the anomalous memory effects are totally destroyed by the magnetic field. We also discuss magnetotransport at very low fields and show that at such fields magnetoresistance is determined by the trajectories having a long Lyapunov region.

Balanced branching in transcription termination.

The theory of stochastic transcription termination based on free-energy competition [von Hippel, P. H. & Yager, T. D. (1992) Science 255, 809-812 and von Hippel, P. H. & Yager, T. D. (1991) Proc. Natl. Acad. Sci. USA 88, 2307-2311] requires two or more reaction rates to be delicately balanced over a wide range of physical conditions. A large body of work on glasses and large molecules suggests that this balancing should be impossible in such a large system in the absence of a new organizing principle of matter. We review the experimental literature of termination and find no evidence for such a principle, but do find many troubling inconsistencies, most notably, anomalous memory effects. These effects suggest that termination has a deterministic component and may conceivably not be stochastic at all. We find that a key experiment by Wilson and von Hippel [Wilson, K. S. & von Hippel, P. H. (1994) J. Mol. Biol. 244, 36-51] thought to demonstrate stochastic termination was an incorrectly analyzed regulatory effect of Mg(2+) binding.