Persistent Memory Effects Research Articles

Using L-cysteine to enhance calibration range and prevent a memory effect in mercury analysis of complex samples via ICP-OES

BackgroundMercury (Hg) is a persistent pollutant occurring in the environment able to transition between different species. It can therefore be found in air, soil and water reservoirs becoming a present concern for the general population but also sensitive populations like pregnant women. Therefore, investigating organ-specific transfer mechanisms of Hg is mandatory for Hg toxicity testing. For this, an in vitro system using microporous inserts to monitor the transfer across an in vitro placental barrier has been used. However, due to the cytotoxicity of Hg only low concentrations (1.26 ×10−4 – 1.36 ×10−2 µg/µL Hg) can be applied, making Hg determination in cell culture medium using inductively coupled plasma-optical emission spectrometry challenging, especially when these trace amounts should be determined alongside other trace elements which are naturally occurring in cells and cell culture medium like the essential metals manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn). Additionally, Hg analysis on an ICP system holds also a number of challenges like a persistent memory effect and instability of Hg standard solutions. MethodsThe development of a rapid and sensitive ICP-OES method to determine Hg in different matrices like cell culture medium and cells has been performed on an Avio 220 Max ICP-OES (Perkin-Elmer) equipped with a cyclonic spray chamber and MicroMist® nebulizer. Cell lysates and cell culture medium were diluted in a mixture of 0.2 % L-cysteine, 2 % HNO3 and 0.1 % HCl and directly introduced into the ICP-OES system. Further method development included the suitability of the analysis of multiple elements like Mn, Fe, Cu, and Zn as well as the determination of the limit of detection and limit of quantification. ResultsThe combination of 0.2 % L-cysteine, 2 % HNO3 and 0.1 % HCl is able to bind and stabilize Hg ions in standard solutions and in biological matrices over a wide dynamic concentration range (1 – 500 µg/L) also alongside other metals like Mn, Fe, Cu and Zn without losses of sensitivity. A short run time of 3 min enables high throughput analysis. Additionally, the high salt and carbon concentrations in the culture medium do not affect Hg sensitivity using the ICP-OES. ConclusionThis method is a useful tool for the quantification of Hg in a variety of complex matrices including cells and cell culture media (high salt and carbon-rich (∼1 % each)) with high sensitivity and minimal sample preparation allowing high throughput. Furthermore, not only Hg can be determined in biological matrices, but even multiple elemental analysis can be carried out to address the effect of Hg on other metals homeostasis.

The Mpemba effect in spin glasses is a persistent memory effect

The Mpemba effect occurs when a hot system cools faster than an initially colder one, when both are refrigerated in the same thermal reservoir. Using the custom-built supercomputer Janus II, we study the Mpemba effect in spin glasses and show that it is a nonequilibrium process, governed by the coherence length ξ of the system. The effect occurs when the bath temperature lies in the glassy phase, but it is not necessary for the thermal protocol to cross the critical temperature. In fact, the Mpemba effect follows from a strong relationship between the internal energy and ξ that turns out to be a sure-tell sign of being in the glassy phase. Thus, the Mpemba effect presents itself as an intriguing avenue for the experimental study of the coherence length in supercooled liquids and other glass formers.

Ferroelectric Self-Poling in GeTe Films and Crystals

Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for spintronics applications. Typically, ferroelectric materials possess random oriented domains that need poling to achieve macroscopic polarization. By using X-ray absorption fine structure spectroscopy complemented with anomalous diffraction and piezo-response force microscopy, we investigated the bulk ferroelectric structure of GeTe crystals and thin films. Both feature multi-domain structures in the form of oblique domains for films and domain colonies inside crystals. Despite these multi-domain structures which are expected to randomize the polarization direction, our experimental results show that at room temperature there is a preferential ferroelectric order remarkably consistent with theoretical predictions from ideal GeTe crystals. This robust self-poled state has high piezoelectricity and additional poling reveals persistent memory effects.

Memory effects in schematic models of glasses subjected to oscillatory deformation

We consider two schematic models of glasses subjected to oscillatory shear deformation, motivated by the observations, in computer simulations of a model glass, of a nonequilibrium transition from a localized to a diffusive regime as the shear amplitude is increased, and of persistent memory effects in the localized regime. The first of these schematic models is the NK model, a spin model with disordered multi-spin interactions previously studied as a model for sheared amorphous solids. The second model, a transition matrix model, is an abstract formulation of the manner in which occupancy of local energy minima evolves under oscillatory deformation cycles. In both of these models, we find a behavior similar to that of an atomic model glass studied earlier. We discuss possible further extensions of the approaches outlined.

Persistent Memory Effects and the Mid- and Post-Brick Dynamic Behaviour of Three-Way Automotive Catalysts

This paper presents the results of an experimental study into the dynamic behaviour of a three-way automotive catalyst and its associated exhaust gas oxygen sensors. Motivated by issues of feedback sensor location, the study seeks to overlay the results of repeat experiments, with sensors and fast-response gas analyzers positioned at different locations, in order to obtain a detailed picture of system dynamics at different points within the catalyst. Initial results demonstrated that the dynamic response of the catalyst can be significantly affected by a persistent memory effect in addition to reversible deactivation dynamics and the familiar oxygen storage/release dynamics of the system. In particular, the effects of prior rich or stoichiometric operation are shown to persist even after extended periods of lean operation. This memory effect is important, not only because of its potential impact on conversion efficiency, but also because of its impact on the repeatability of experiments carried out under what would appear to be near-identical operating conditions. By pre-conditioning under rich conditions highly repeatable experiments were achieved. The results were combined to give a detailed picture of catalyst dynamics at pre-, mid- and post-catalyst locations, and provide insight into catalyst and (non-ideal) exhaust gas oxygen sensor behavior.

Persistent Memory Effects and Pre-Conditioning For Repeatable Investigations Into Three-Way Catalyst Dynamics

Abstract This paper presents the results of an experimental study into the dynamic behaviour of a three-way automotive catalyst. The study suggests that the dynamic response of the catalyst can be significantly affected by a persistent memory effect in addition to the familiar oxygen storage / release dynamics of the system. In particular, the effects of prior rich or stoichiometric operation are shown to persist even after extended periods of lean operation. This memory effect is important, not only because of its potential impact on conversion efficiency, but also because of its impact on the repeatability of experiments carried out under what would appear to be similar operating conditions.

Spatial Memory Is Intact in Aged Rats After Propofol Anesthesia

We have previously demonstrated that aged rats have persistent impairment of spatial memory after sedation with nitrous oxide or general anesthesia with isoflurane-nitrous oxide. Propofol has different receptor mechanisms of action and a favorable short-term recovery profile, and it has been proposed that propofol is devoid of enduring effects on cognitive performance. No studies have investigated this question in aged subjects, however, so we designed an experiment to examine the long-term effects of propofol anesthesia on spatial working memory. Eighteen-mo-old rats were randomized to 2 h of 100% oxygen-propofol anesthesia (n=11) or to a control group that breathed 100% oxygen (n=10). Propofol was administered by continuous infusion via a tail vein catheter. Rats breathed spontaneously and rectal temperature was maintained. Mean arterial blood pressure was measured noninvasively and a venous blood gas was obtained just before discontinuation of propofol. After a 2-day recovery, spatial working memory was assessed for 14 days using a 12-arm radial maze. The number of total errors, number of correct choices to first error, and time to complete the maze was recorded and analyzed using a repeated measure analysis of variance (ANOVA), with P<0.05 being considered statistically significant. The average propofol infusion rate was 0.6+/-0.1 mg.kg (-1).min(-1), a rate corresponding to a 50% effective concentration dose in adult rats. Mean arterial blood pressure during anesthesia was 100+/-2 mm Hg and venous blood gases remained in the normal range. There was no difference between the control and previously anesthetized rats on any measure of radial arm maze performance, indicating propofol anesthesia produces no lasting impairment in spatial working memory in aged rats. In aged rats, propofol anesthesia is devoid of the persistent memory effects observed with other general anesthetics in this model. Thus, while it appears that the state of general anesthesia is neither necessary nor sufficient for development of postanesthetic memory impairment, the choice of anesthetics may play a role in late cognitive outcome in the aged.

Memory effect of diethylamine mobile phase additive on chiral separations on polysaccharide stationary phases.

The existence of a memory effect for amine additives on polysaccharide chiral stationary phases has often been suggested, but not clearly demonstrated. Demonstration of this effect is made difficult by the uncertainty as to which analytes benefit from use of amine additives and, typically, an unclear history of column use. In this work, analytes were selected for differences in their behavior with and without additives. Columns were used with no prior history. A persistent memory effect was demonstrated on a CHIRALPAK AD-H column in hexane-based mobile phases. This effect was short-lived, with polar organic mobile phases. Memory was short-lived on a CHIRALCEL OJ-H column. Flushing with isopropanol was shown to remove most of the memory effect. Compounds expected to require amine additives on CHIRALCEL OD-H column did not. Acid treatment of the AD-H and OD-H columns changed their performance, which was subsequently restored by the incorporation of amine.

Memory effects and slow dynamics in ultra thin magnetic films

Monte Carlo studies of a uniaxial spin system on a square lattice with both ferromagnetic exchange interactions and dipolar interactions reveal three distinct dynamical regimes at low temperatures. In the first regime the magnetization decays through nucleation and growth of spin islands, in the second regime, despite the magnetization being effectively zero, there is a persistent memory effect most clearly revealed by the asymmetry between the numbers of up and down islands. The third regime is characterized by slow crystallization of the equilibrium smectic phase from the quenched polycrystalline state.

Acceleration-induced nonlocal electrodynamics in Minkowski spacetime

We discuss two nonlocal models of electrodynamics in which the nonlocality is induced by the acceleration of the observer. Such an observer actually measures an electromagnetic field that exhibits persistent memory effects. We compare Mashhoon's model with a new ansatz developed here in the framework of charge & flux electrodynamics with a constitutive law involving the Levi-Civita connection as seen from the observer's local frame and conclude that they are in partial agreement only for the case of constant acceleration.

Precipitation of Tellurium‐Rich Phase in Heavily Diethyltellurium‐Doped GaAs during Organometallic Vapor Phase Epitaxy

layers were heavily doped with liquid source diethyltellurium (DETe) during organometallic vapor phase epitaxy. Samples were characterized by Hall effect measurements and transmission electron microscopy (TEM). The electron concentration was observed to saturate at for high DETe flows, which is independent of growth temperature in the investigated range from 475 to 600°C. TEM examination revealed the presence of precipitates in layers doped above the saturation level. The precipitates were Te‐rich by energy dispersive x‐ray analysis. Electron diffraction study showed that they have the zinc‐blende structure with a lattice constant of 6.5 Å. The appearance of tellurides at high doping levels indicates that the formation of a second phase could be one of the main mechanisms responsible for the carrier saturation in Te‐doped . The liquid source DETe causes persistent memory effects associated with the adsorption of DETe on the stainless steel tube walls of the gas distribution system.

Determination of 99Tc in nuclear samples by inductively coupled plasma mass spectrometry

Different approaches for the determination of 99Tc in various nuclear samples are described. Technetium has been determined in leachates of spent fuel and vitrified highly active waste using the elemental response curve of the instrument. It has been observed that Tc is preferentially leached from spent fuel under oxidizing conditions (30% H2O2) indicating that the pertecnectate ion should be the leached species. It has also been determined in spent fuel dissolver solutions by the method of standard additions using other elements present in the sample as internal standards. Zirconium, Mo and Ru showed to be adequate internal standards for the determination of Tc in those samples. The formation of several polyatomic ions containing Tc was observed at high Tc concentrations. Peaks at m/z 115, 131 and 147 were assigned to TcO+, TcO2+ and TcO3+, the TcO2+ being the predominant polyatomic ion. The ratios of the polyatomic ion to the main 99Tc peak were estimated with the help of Rh as internal standard. The influence of plasma operating conditions on the relative abundance of those polyatomic ions has been studied. It was also observed that Tc suffers from a long and persistent memory effect.