Correlation Time Research Articles

Survival Probability, Particle Imbalance, and Their Relationship in Quadratic Models

We argue that the dynamics of particle imbalance in quadratic fermionic models is, for the majority of initial many-body product states in the site occupation basis, virtually indistinguishable from the dynamics of survival probabilities of single-particle states. We then generalize our statement to a similar relationship between the non-equal time and space density correlation functions in many-body states, and the transition probabilities of single-particle states at nonzero distances. Finally, we study the equal-time connected density–density correlation functions in many-body states, which exhibit certain qualitative analogies with the survival and transition probabilities of single-particle states. Our results are numerically tested for two paradigmatic models of single-particle localization: the 3D Anderson model and the 1D Aubry–André model. This work gives an affirmative answer to the question of whether it is possible to measure features of single-particle survival and transition probabilities by the dynamics of observables in many-body states.

Asymmetry of winter precipitation event predictions in South China

AbstractWinter precipitation anomalies in South China (SC) frequently result in severe disasters. However, the evaluation of prediction performance and distinctions between positive precipitation anomaly events (PPA, wet condition) and negative precipitation anomaly events (NPA, dry condition) in current operational models remains incomplete. This study employed the Climate Forecast System version 2 (CFSv2) to assess winter precipitation prediction accuracy in SC from 1983 to 2021. Differences in predicting PPA and NPA events and the underlying physical mechanisms were explored. The results indicate that CFSv2 can effectively predict interannual variations in winter precipitation in SC, as there is a significant time correlation coefficient of 0.68 (0.62) between observations and predictions, with a lead time of 0 (3) months. The model revealed an intriguing asymmetry in prediction skills: PPA outperformed NPA in both deterministic and probabilistic prediction. The higher predictability of PPA, as indicated by the perfect model correlation and signal-to-noise ratio, contributed to its superior prediction performance when compared to NPA. Physically, tropical signals from the ENSO and extratropical signals from the Arctic sea ice anomaly, were found to play pivotal roles in this asymmetric feature. ENSO significantly impacts PPA events, whereas NPA events are influenced by a complex interplay of factors involving ENSO and Arctic sea ice, leading to low NPA predictability. The capability of the model to replicate Arctic sea ice signals is limited, but it successfully predicts ENSO signals and reproduces their related circulation responses. This study highlights the asymmetrical features of precipitation prediction, aiding in prediction models improvement.

Analysis of financial markets by coupled criticality approach

Analysis of the criticality in finance and economics is an important topic for scholars. The crises are conditions in which unpredictable behavior have been emerged. On the other hand, the contagion from one market to another one due to the complex nature of them is a crucial concept. Therefore, we should consider economies and financial markets as entangled systems that interact with each other, and studying one’s behavior without considering its interacting structures will not provide us with adequate information. In this paper, we have considered the critical states of some emerging and mature markets’ indices. S&P500 and Nikkei 225 as representatives of mature markets, and SSE Composite and TEDPIX as representatives of emerging markets have been analyzed. Coupled criticality emerges when two interacting systems reach their critical state due to their interactions. One of the efficient methods to study the coupled criticality is the bi-variate multifractal random walk model. This method is useful to assess the correlation of rare events and coupled criticality in entangled systems such as financial markets. The observations in this paper show that TEDPIX and S&P500 have higher critical states among others in most time lags by assessing criticality parameter explained in the model, and in longer time lags criticality parameter decreases in all indices. Coupled criticality parameter explained in the model is assessed between each index mentioned and TEDPIX. Results show that TEDPIX and S&P500 have the highest level of coupled criticality. To figure out how long-range time correlation between rare events in each index affect its critical behavior, the data of each index are shuffled, and the criticality parameter is calculated for the shuffled data. From the observations, it can be concluded that this matter has more substantial effect on mature markets. As it is known, shuffling removes the effect of the long-range time correlations. Therefore, the coupled criticality parameter is calculated for the shuffled S&P500 data and TEDPIX. Results show that the long-range correlation of S&P500 data has a significant effect on the coupled criticality behavior of S&P500 and TEDPIX.

3D Printed Drug Delivery Systems in Action-Magnetic Resonance Imaging and Relaxometry for Monitoring Mass Transport Phenomena.

The hypothesis of the study was that (1) 3D printed drug delivery systems (DDS) could be characterized in situ during drug release using NMR/MRI techniques in terms of mass transport phenomena description (interfacial phenomena), particularly for systems dealing with two mobile phases (e.g., water and low molecular weight liquid polymer); (2) consequently, it could be possible to deduce how these interfacial mass transport phenomena influence functional properties of 3D printed DDS. Matrix drug delivery systems, prepared using masked stereolithography (MSLA), containing poly(ethylene glycol) diacrylate (PEGDA) and low molecular weight polyethylene glycol (PEG) with ropinirole hydrochloride (RH) were studied as example formulations. The PEGDA to PEG (mobile phase) concentration ratio influenced drug release. It was reflected in spatiotemporal changes in parametric T2 relaxation time (T2) and amplitude (A) images obtained using magnetic resonance imaging (MRI) and T1-T2 relaxation time correlations obtained using low-field time-domain nuclear magnetic resonance (LF TD NMR) relaxometry during incubation in water. For most of the tested formulations, two signal components related to PEG and water were assessed in the hydrated matrices by MRI relaxometry (parametric T2/A images). The PEG component faded out due to outward PEG diffusion and was gradually replaced by the water component. Both components spatially and temporally changed their parameters, reflecting evolving water-polymer interactions. The study shows that dynamic phenomena related to bidirectional mass transport can be quantified in situ using NMR and MRI techniques to gain insight into drug release mechanisms from 3D printed DDS systems.

A Monte Carlo simulation of tracer diffusion in amorphous polymers.

Tracer diffusion in amorphous polymers is a sought-after quantity for a range of technological applications. In this regard, a quantitative description of the so-called decoupling from the reverse proportionality between viscosity and diffusion coefficient into a fractional one remains a challenge requiring a deeper insight. This work employs a Monte Carlo simulation framework in 3 dimensions to investigate the consequences of different scenarios for estimating this fractional exponent on the diffusion coefficient of tracers in polymers near glass transition. To this end, we adopted a continuous-time random walk model for tracer diffusion in the supercooled liquid state. The waiting time distribution of the diffusants was computed based on the rotational correlation times of the polymer. This proposed procedure is of particular interest because it brings the quantity of waiting time (and its statistics) in connection with the measurable observable of rotational times. In the framework of our simulations the aforementioned fractional exponent appears in the relation between the diffusant's waiting time and the rotational time of the diffusion medium. A limited comparison with experimental diffusivities from the literature revealed a reasonable agreement with a fractional exponent on the basis of the molar volumes of the diffusant and the monomeric unit. Finally, an analysis of time-averaged mean squared displacement pointed to normal Brownian dynamics for tracer diffusion in polymers above the glass transition temperature.

Effect of colored noise on precursors of thermoacoustic instability in model gas turbine combustors

In this work, we numerically investigate the dynamics of a prototypical thermoacoustic system, the generalized Van der Pol oscillator, in the presence of additive noise of varying color (correlation time) and intensity while the system undergoes supercritical and subcritical Hopf bifurcation. We specifically investigate the influence of noise color on trends in the coherence factor and the Hurst exponent in the subthreshold region to assess their reliability as instability precursors. The Hurst exponent is found reliable only for correlation times much larger than the time scale of the instability while the coherence factor is found to be reliable for the entire range of noise color investigated. These inferences are found to hold for both supercritical and subcritical bifurcation cases.

Collective dynamics of liquid sulphur across the polymerisation transition temperature probed by inelastic x-ray scattering

Inelastic x-ray scattering (IXS) experiments on liquid sulphur were carried out below (140 ∘C) and above (180 ∘C) the polymerisation temperature T λ of about 159 ∘C to investigate changes in the collective dynamics of this unique liquid, that exhibits a liquid–liquid transition. As reported earlier, broad longitudinal acoustic excitation signals were observed at both temperatures, and only the width of the quasielastic peaks slightly decreased when the temperature crossed the transition temperature. A model analysis was performed using a generalised Langevin formalism with a memory function having one thermal and two viscoelastic decay channels with the help of simple sparse modelling, and large positive deviations from the hydrodynamic sound velocity by 51%–54% were observed. The fast viscoelastic relaxation time τ µ is close to the correlation times of intermolecular stretching and bending motions of local sulphur connections in both ring and chain structures, and is similar to those of other molecular liquids. The small contrasts in the IXS spectra across the λ transition result in large changes in only the slow viscoelastic decay time τ α of the memory function. The τ α value at 140 ∘C matches the mixed internal/external torsional modes of S8 molecules well, whereas that at 180 ∘C has no corresponding molecular motion mode. The kinematic viscosity values at the Q→0 limit are much smaller than the minimum values of macroscopic shear viscosity, indicating that large changes in relaxation dynamics are expected with Q in the GHz and MHz excitation regimes.

Intestinal Ultrasonography as an Alternative to Fecal Calprotectin to Monitor Patients with Crohn's Disease: Experience from a Novice Sonographer.

While fecal calprotectin (Fcal) is now recommended, the positioning of intestinal ultrasonography (IUS) is still unknown to monitor patients with CD. To assess the agreement between IUS performed by a novice sonographer and Fcal to detect active CD and to compare these two monitoring tools to determine the need for therapeutic escalation. In this cross-sectional prospective study, we consecutively included CD patients ≥ 18years-old with concomitant IUS and Fcal testing within 7days. IUS was performed by a novice sonographer. The endpoints were the agreement between IUS and Fcal (> 150µg/g) to detect active CD and the need for therapeutic escalation. Among 66 patients undergoing IUS, 56 patients had also Fcal testing. The agreement between IUS and Fcal to detect an active CD was 80.4% (κ-coefficient = 0.536 ± 0.127). Fcal, IUS or both had respectively the following positive (76.9%[54.0-99.8], 70.0%[49.9-90.1], and 81.8%[59.0-100.0]) and negative (81.4%[69.8-93.0], 88.9%[78.6-99.2], and 80.0%[68.3-91.7]) predictive values to detect active CD requiring therapeutic escalation. Using a 10 points-acceptability numerical scale, IUS presented with a better acceptability than Fcal (9.5 ± 1.2 vs 8.0 ± 2.3, p < 0.0001). Contrary to the agreement with Fcal and the performances of IUS to identify the need for therapeutic escalation, the duration of IUS procedure decreased over time (correlation coefficient = -0.54, p = 0.001) and plateaued between 15 and 20min-long from the 24th procedure. IUS and fecal calprotectin do not give the same information and could be complementary to monitor patients with CD.

Retinoblastoma patients treated in Sri Lanka from 2014 to 2020: epidemiology, clinical status and correlates of lag time in seeking tertiary care services

BackgroundRetinoblastoma (RB) is a tumour of children < 5 years with a incidence of 1 in 20,000. Around 20 RB cases are diagnosed yearly in Sri Lanka, a lower middle-income country with high literacy levels and healthcare free at point of delivery. Incidence, local and systemic severity and mortality related to RB are reportedly high in low- and middle- income countries in comparison to higher income countries. Aims of this study were to describe demographic, socioeconomic, and clinical characteristics of Sri Lankan RB patients attending the designated RB unit at the Lady Ridgeway Hospital (LRH), Colombo between January 2014 to December 2020, and determine correlates of lag time (LT) for first tertiary care visit after detecting the first symptom/sign.MethodsTwo descriptive cross-sectional studies (DCSS) were conducted, one on 171 RB patients with demographic and clinical data collected between 2017 and 2020. In 2021, the second DCSS took place where socioeconomic and further demographic data were collected using telephone interviews, recruiting a subgroup of 90 (53%), consenting and contactable RB patient/ parent pairs. Bivariate and multivariable analyses were applied to determine correlates of LT of > 4 weeks for first tertiary care visit. Results were expressed as odds ratios and 95% confidence intervals.ResultsLRH survey (N = 171): Median age at diagnosis was 15 months (range 1–94 months; IQR: 8–27); 89 (52%) were females. Groups D and E tumours were 25.7% (n = 44) and 62.6% (n = 107) respectively with 121 (71%) enucleations. The number of deaths were 2 (1.2%). Telephone survey (N = 90): Proportion with LT of > 4 weeks for first tertiary care visit was 58% (n = 52). None of the putative risk factors (ethnicity, parental educational level, socioeconomic status, distance from residence to tertiary care unit and receiving financial assistance) were associated with LT in both analyses.ConclusionDespite a high proportion with groups D and E tumours and enucleations, mortality rate was low, most likely due to availability of designated tertiary care. No correlates for LT of > 4 weeks for tertiary care presentation were identified. Early RB detection needs rigorous implementation of screening strategies and increased awareness among primary care health workers and parents.

Distribution characteristics of radiant heat flux on tank surfaces exposed to wildland fires

AbstractThe expansion of wildland‐urban interface tends to expose fuel tanks to wildland fires, the frequency and intensity of which have increased in recent years due to climate change and global warming. This study aims to examine the distribution of radiant heat flux on a tank surface exposed to a wildland fire front, with a particular focus on extreme wildland fires. A theoretical framework is proposed, which consists of a flame length correlation, a thermal radiation model, and a correlation of time to failure, to calculate the radiant heat flux received by the tank surface and the potential for tank failure. The horizontal and circumferential distribution characteristics of the radiant heat flux are intensively discussed, in terms of the heat flux profile, heating area, total heat, time to failure versus the fireline intensity, fireline width, spacing, and tank volume. In particular, extreme wildland fires, characterized by large fireline intensities, could potentially destroy the tank within the safety spacing mandated by the current regulations. Therefore, a comparison between the time to failure and the radiant heating duration is suggested to ascertain the necessary safety spacing. The uncertainties in model calculations are also addressed, which arise from the use of different flame length correlations and flame radiative fractions.

Integrating Electroencephalography with Motophysic training: Assessing the shift in fitness and cognitive functions in elite youth soccer players

Motor and physical fitness play a crucial role to optimize the player performance in the soccer game. Implementing a customized workout schedule targeting Motophysic Fitness (MPF) helps to elevate their on-field performance. The present study was aimed to assess the impact of a 12-week MPF Training program targeted to have improvements in physical fitness for elite soccer players. MPF training program was implemented during the off-season for youth soccer players with average age (20 ± 1 years), height (1.75 ± 0.5 m) weight (64.3 ± 5.7 kg). Soccer-related fitness traits were assessed to evaluate performance levels, while Electroencephalography (EEG) was utilized for cognitive assessment. Statistical analysis was performed to evaluate the outcome of the fitness traits. Significant improvements were observed across diverse fitness traits, with mean values increasing by a minimum of 2 % and a maximum of 5 %. Speed emerged as a predominant contributor, showing a robust correlation (Adjusted R2 = 0.84), while agility, strength, power, endurance, balance, coordination, and reaction time also displayed substantial improvements. Despite observable gains in flexibility, its impact on overall fitness appeared comparatively modest (Adjusted R2 = 0.23). Z-test confirmed the statistical significance of all fitness assessments post-MPF, with p-values less than 0.05 for each test. Features extracted from EEG highlighted the improvement in cognitive ability before and after training.

Different factors affecting the real estate market in the Egyptian context

Purpose Real estate projects are capital-intensive and deeply intertwined with economic factors, making them subject to various influences besides local housing needs. This paper aims to comprehensively understand the dynamics of the Egyptian real estate market, examining real estate cycles, driving factors and their correlation and scale of impact. Design/methodology/approach The study conducts a literature review to explore real estate cycles and their driving factors, along with the relationship between real estate and macroeconomic cycles. It then delves into the dynamics of the Egyptian real estate market, followed by a time series analysis that incorporates five key indicators: economic indicator, demand indicator, supply indicator, capital flow indicator and cost indicator over a 12-year interval (2012–2023), to examine short-term cycle factors, followed by correlation and multi-linear regression analysis to elucidate interrelations among these factors. Findings Through measuring and comparing the prementioned indicators with different economic and social events, the study paints a comprehensive picture of the macroeconomic environment and the real estate cycle in Egypt. Where demand has been found to be more sensitive and directly affected by macroeconomic factors than the supply. With the economic factor as the factor with the highest impact, especially in times of economic fluctuations, the impact has been immediate and short-term. These findings support the idea that the demand in Egypt is speculative, laying a threat of longer recession periods in the long term and having greater and more direct impact. Originality/value This paper contributes to the understanding of the Egyptian real estate market by integrating insights from real estate cycles, macroeconomics and specific market dynamics. The application of time series, correlation and multi-linear regression analysis provides a nuanced understanding of the interplay between several factors shaping the real estate cycle. Ultimately, the findings offer valuable insights for decision-makers involved in urban development planning, facilitating more informed and precise decision-making processes.

Theoretical study of vibronic absorption spectra and Franck-Condon factors of copper and silver hydrides

The electronic absorption spectra of CuH and AgH molecules are calculated using the analytical expression for the spectral density related to the thermal dipole time correlation function. In addition, the vibronic transition probabilities between the initial and final states are determined by calculating the transition dipole moments and the Franck-Condon factors using the LEVEL program. The spectroscopic constants recently obtained from MRCI + SOC calculations are used to calculate the absorption spectral line shapes of CuH and AgH molecules and plotted in the time and frequency domains for the vibronic transitions from the ground state Ω = 0+(I) to the excited states Ω = 0+(II), 0+(III), 1(I), 1(II), 1(III), and 1(IV) for CuH and to the excited states Ω = 0+(II), 0+(III), 0+(IV), 1(II), 1(III), 1(IV), 1(V), and 1(VI) for AgH.

Parsing Dynamics of Protein Backbone NH and Side-Chain Methyl Groups using Molecular Dynamics Simulations.

Experimental NMR spectroscopy and theoretical molecular dynamics (MD) simulations provide complementary insights into protein conformational dynamics and hence into biological function. The present work describes an extensive set of backbone NH and side-chain methyl group generalized order parameters for the Escherichia coli ribonuclease HI (RNH) enzyme derived from 2-μs microsecond MD simulations using the OPLS4 and AMBER-FF19SB force fields. The simulated generalized order parameters are compared with values derived from NMR 15N and 13CH2D spin relaxation measurements. The squares of the generalized order parameters, S2 for the N-H bond vector and Saxis2 for the methyl group symmetry axis, characterize the equilibrium distribution of vector orientations in a molecular frame of reference. Optimal agreement between simulated and experimental results was obtained by averaging S2 or Saxis2 calculated by dividing the simulated trajectories into 50 ns blocks (∼five times the rotational diffusion correlation time for RNH). With this procedure, the median absolute deviations (MAD) between experimental and simulated values of S2 and Saxis2 are 0.030 (NH) and 0.061 (CH3) for OPLS4 and 0.041 (NH) and 0.078 (CH3) for AMBER-FF19SB. The MAD between OPLS4 and AMBER-FF19SB are 0.021 (NH) and 0.072 (CH3). The generalized order parameters for the methyl group symmetry axis can be decomposed into contributions from backbone fluctuations, between-rotamer dihedral angle transitions, and within-rotamer dihedral angle fluctuations. Analysis of the simulation trajectories shows that (i) backbone and side chain conformational fluctuations exhibit little correlation and that (ii) fluctuations within rotamers are limited and highly uniform with values that depend on the number of dihedral angles considered. Low values of Saxis2, indicative of enhanced side-chain flexibility, result from between-rotamer transitions that can be enhanced by increased local backbone flexibility.

Time‐frequency domain correlation method based on the synchrosqueezed wavelet transform for tunnel vibroseis and its application

AbstractTo meet the demand for long‐distance and highly accurate detection in tunnel construction, a vibroseis source has been introduced into tunnel forward prospecting. However, serious noise in tunnels reduces the resolution of vibroseis signals, and small‐scale structure recognition in tunnels requires higher signal resolution. Thus, we develop a time‐frequency domain correlation method based on the synchrosqueezed wavelet transform for tunnel vibroseis data. Time‐frequency domain correlation may capture more information than a single time or frequency domain correlation method, and its effectiveness depends on the time‐frequency transformation method. The synchrosqueezed wavelet transform allows us to obtain high‐resolution time‐frequency spectra and thus helps to extract high‐resolution effective signals. The advantages and disadvantages of different correlation methods are highlighted using numerical examples, in which the high resolution and strong robustness of the time‐frequency domain correlation method based on the synchrosqueezed wavelet transform are demonstrated. A detailed field case study in an iron mine tunnel further demonstrates the reliability of the time‐frequency domain correlation method based on the synchrosqueezed wavelet transform for practical data.

Escape rate of a dimer under the influence of additive colored noise: Ornstein–Uhlenbeck process

We consider the problem of a dimer consisting of two monomers held together by a combination of a harmonic and a Morse potential in a bi-stable potential via an additive-colored Ornstein–Uhlenbeck (OU) noise. We investigated the problem for different values of the harmonic spring constant, κ, and observe a non-monotonic dependent of the escape rate with respect to the harmonic spring constant, κ. However, the escape rate decreases exponentially with respect to the correlation time, τ of the OU noise, i.e., an increase in the correlation time of the noise causes a delay in the escape mechanism of the dimer. Another important observation is the shift in the optimal spring constant, kopt, of the dimer with respect to an increase in the correlation time, τ. It was observed that for different τ values, there is a shift in the kopt values. In summary, a complex interplay between the harmonic force and the correlation time of the OU noise is involved in the escape process of the dimer.

Robust Methods for Assessing the Characteristics of Locomotor Activity Based on Markerless Video Capture Data

Introduction. Analysis of locomotor activity is essential in a number of biomedical and pharmacological research designs, as well as environmental monitoring. The movement trajectories of biological objects can be represented by time series exhibiting a complex multicomponent structure and non-stationary dynamics, thus limiting the effectiveness of conventional correlation and spectral time series analysis methods. Recordings obtained using markerless technologies are typically characterized by enhanced noise levels, including both instrumental noise and anomalous errors associated with false estimates of the location of the points of interest, as well as gaps in the trajectories, promoting an urgent need in the development of robust methods to assess the characteristics of locomotor activity.Aim. Development of robust methods for assessing the characteristics of locomotor activity capable of efficient processing of noisy recordings obtained by markerless video-based motion capture systems.Materials and methods. In order to assess the characteristics of locomotor activity, the relative movements of body parts of laboratory animals were analyzed using the stability metrics of the mutual dynamics of their trajectories, their relative delays, as well as the relative duration of the recording fragments when relatively stable mutual dynamics could be observed. The local maxima of the cross-correlation function of two body fragments, the minima of the standard deviation of the difference between their Hilbert phases, as well as their relative delays, were used as the metrics of mutual dynamics.Results. The considered phase metrics were shown to explicitly reflect changes in locomotor activity, while the assessment of time delays using phase metric was shown to be prone to periodic error. The above limitation could be largely overcome using the correlation metrics, assuming that phase and correlation metrics could be combined.Conclusion. The proposed robust methods provide stable estimates of the characteristics of locomotor activity based on markerless video capture recordings, altogether increasing the efficiency of diagnostic procedures and assessment of the therapeutic effect during rehabilitation.

Orientation time correlation functions up to the fourth cumulant for liquid water

The orientation time correlation functions (OTCFs) of molecular liquids are related to many experimental observations but subtle in theoretical calculations. Usually, the OTCFs at different timescales are described by distinct approaches. The OTCFs at short times were expanded into a series in an order of molecular angular velocity components, and the second cumulant (SC) of the series gave a single-frequency integral over one-mode propagation function weighted by a rotational density of states (DOS) of the liquid, whereas the OTCFs at long times displayed an exponential decay according to the Debye theory. In this paper, we derived the series of the OTCFs up to the fourth cumulant (FC), which gave a sum of twofold frequency integrals over two-mode propagation functions weighted by a product of two rotational DOSs associated with one or two molecular axes. With no need of any fitting parameter, the OTCFs calculated up to the SC and up to the FC were compared with simulation results for liquid water. With the power spectra of angular velocity autocorrelation function, which have a finite value at zero frequency, as the inputs, the OTCFs in both SC and FC schemes resulted in an exponential decay at long times, while the decay times were smaller than the simulation values. The positive results were the calculations with stable rotational instantaneous-normal-mode spectra, which have a linear behavior extrapolated to zero at low frequencies. As the stable rotational INM spectra were used as the inputs, the OTCFs in the SC scheme produced a slow power-law decay, but the OTCFs in the FC scheme captured the simulation behaviors from short to long timescale, including an exponential decay, with the decay times of the 2nd-rank OTCFs close to the simulation values.

Study of the effect of ethanol on the properties of poloxamer 338 solutions by rotational viscometry and spin probe method

The aim. Study the properties of 20 % solutions of poloxamer 338 (P338) in water and mixed solvents water-ethanol using rotational viscometry and the spin probe method at various temperatures. Materials and methods. 20 % m/m solutions of P338 in water and water – ethanol mixtures were the objects of research. The solutions were studied by rotational viscometry at various temperatures; the flow behaviour, lower yield stress (t0) and dynamic or apparent viscosity (η) were determined. Spin probes based on fatty acids, which differ in molecular structure, solubility, and radical localization, were added to the solutions. Electron paramagnetic resonance (EPR) spectra were obtained to determine their type and parameters. Results. Depending on the content, ethanol affects the rheological properties of 20 % solution of P338. The solution was demonstrated to be able to thermally induce sol → gel transition at 32 °C when ethanol content is 5 % m/m. The rheological parameters of the gel at 32 °C and 37 °C exhibit an increase (in comparison to the gel without ethanol), accompanied by a reduction in the packing density of polypropylene oxide (PPO) chains within the cores of P338 micelles. At an ethanol content of 10 % m/m, the gel formation temperature rises to 40 °C. At ethanol content of 15 % m/m and above, 20 % P338 solutions do not form gels at temperatures between 25 °C and 40 °C. The values of rotational correlation times (τ) and the order parameter (S) of fatty acid-based spin probes were observed to decrease with increasing ethanol content up to 30 % m/m; in the case of the ammonium salt of 5‑doxylstearic acid (5-DSA NH4 salt), the anisotropic EPR spectra transform, becoming a superposition of two triplets and subsequently a triplet. P338 solutions retain their ability to undergo thermally induced sol ↔ gel transitions as long as the EPR spectra of this probe exhibit anisotropy at temperatures ranging from 25 °C to 37 °C. As the concentration of ethanol in the solution increases, the solvation of the cores of P338 micelles by the dispersion medium of the solution also increases. Conclusions. It was demonstrated that ethanol, when added to the 20 % P338 solution, results in changes to the rheological properties of this solution. However, at the ethanol content of 5-10 % m/m, the ability of P338 to thermally induce sol → gel transition remains unaltered. The rheological properties of the 20 % P338 solution exhibit a correlation with the observed change in EPR spectra types for the 5-DSA NH4 salt. As the ethanol content in the solution increases, the solvation of P338 micelle cores by the dispersion medium increases, accompanied by decreased density and orderliness of the PPO chains packing in the micelle cores

Study of the effect of ethanol on the properties of poloxamer 338 solutions by rotational viscometry and spin probe method

The aim. Study the properties of 20 % solutions of poloxamer 338 (P338) in water and mixed solvents water-ethanol using rotational viscometry and the spin probe method at various temperatures. Materials and methods. 20 % m/m solutions of P338 in water and water – ethanol mixtures were the objects of research. The solutions were studied by rotational viscometry at various temperatures; the flow behaviour, lower yield stress (t0) and dynamic or apparent viscosity (η) were determined. Spin probes based on fatty acids, which differ in molecular structure, solubility, and radical localization, were added to the solutions. Electron paramagnetic resonance (EPR) spectra were obtained to determine their type and parameters. Results. Depending on the content, ethanol affects the rheological properties of 20 % solution of P338. The solution was demonstrated to be able to thermally induce sol → gel transition at 32 °C when ethanol content is 5 % m/m. The rheological parameters of the gel at 32 °C and 37 °C exhibit an increase (in comparison to the gel without ethanol), accompanied by a reduction in the packing density of polypropylene oxide (PPO) chains within the cores of P338 micelles. At an ethanol content of 10 % m/m, the gel formation temperature rises to 40 °C. At ethanol content of 15 % m/m and above, 20 % P338 solutions do not form gels at temperatures between 25 °C and 40 °C. The values of rotational correlation times (τ) and the order parameter (S) of fatty acid-based spin probes were observed to decrease with increasing ethanol content up to 30 % m/m; in the case of the ammonium salt of 5‑doxylstearic acid (5-DSA NH4 salt), the anisotropic EPR spectra transform, becoming a superposition of two triplets and subsequently a triplet. P338 solutions retain their ability to undergo thermally induced sol ↔ gel transitions as long as the EPR spectra of this probe exhibit anisotropy at temperatures ranging from 25 °C to 37 °C. As the concentration of ethanol in the solution increases, the solvation of the cores of P338 micelles by the dispersion medium of the solution also increases. Conclusions. It was demonstrated that ethanol, when added to the 20 % P338 solution, results in changes to the rheological properties of this solution. However, at the ethanol content of 5-10 % m/m, the ability of P338 to thermally induce sol → gel transition remains unaltered. The rheological properties of the 20 % P338 solution exhibit a correlation with the observed change in EPR spectra types for the 5-DSA NH4 salt. As the ethanol content in the solution increases, the solvation of P338 micelle cores by the dispersion medium increases, accompanied by decreased density and orderliness of the PPO chains packing in the micelle cores