Memory Effect, Rejuvenation and Chaos Effect in the Multi-layer Random Energy Model

We introduce magnetization to the Multi-layer Random Energy Model which has a hierarchical structure, and perform Monte Carlo simulation to observe the behavior of ac-susceptibility. We find that this model is able to reproduce three prominent features of spin glasses, i.e., memory effect, rejuvenation and chaos effect, which were found recently by various experiments on aging phenomena with temperature variations.Comment: 10 pages, 14 figures, to be submitted to J. Phys. Soc. Jp

Scaling Law and Aging Phenomena in the Random Energy Model

We study the effect of temperature shift on aging phenomena in the Random Energy Model (REM). From calculation on the correlation function and simulation on the Zero-Field-Cooled magnetization, we find that the REM satisfies a scaling relation even if temperature is shifted. Furthermore, this scaling property naturally leads to results obtained in experiment and the droplet theory.Comment: 8 pages, 7 figures, to be submitted to J. Phys. Soc. Jp

Numerical Study of Aging in the Generalized Random Energy Model

Magnetizations are introduced to the Generalized Random Energy Model (GREM) and numerical simulations on ac susceptibility is made for direct comparison with experiments in glassy materials. Prominent dynamical natures of spin glasses, {\it i.e.}, {\em memory} effect and {\em reinitialization}, are reproduced well in the GREM. The existence of many layers causing continuous transitions is very important for the two natures. Results of experiments in other glassy materials such as polymers, supercooled glycerol and orientational glasses, which are contrast to those in spin glasses, are interpreted well by the Single-layer Random Energy Model.Comment: 8 pages, 9 figures, to be submitted to J. Phys. Soc. Jp

Monitoring microplastics in the atmosphere and cryosphere in the circumpolar North: A case for multi-compartment monitoring

The atmosphere and cryosphere have recently garnered considerable attention due to their role in transporting microplastics to and within the Arctic, and between freshwater, marine, and terrestrial environments. While investigating either in isolation provides valuable insight on the fate of microplastics in the Arctic, monitoring both provides a more holistic view. Nonetheless, despite the recent scientific interest, fundamental knowledge on microplastic abundance, and consistent monitoring efforts, are lacking for these compartments. Here, we build upon the work of the Arctic Monitoring and Assessment Programme’s Monitoring Guidelines for Litter and Microplastic to provide a roadmap for multi-compartment monitoring of the atmosphere and cryosphere to support our understanding of the sources, pathways, and sinks of plastic pollution across the Arctic. Overall, we recommend the use of existing standard techniques for ice and atmospheric sampling and to build upon existing monitoring efforts in the Arctic to obtain a more comprehensive pan-Arctic view of microplastic pollution in these two compartments

Off-Equilibrium Dynamics in Finite-Dimensional Spin Glass Models

The low temperature dynamics of the two- and three-dimensional Ising spin glass model with Gaussian couplings is investigated via extensive Monte Carlo simulations. We find an algebraic decay of the remanent magnetization. For the autocorrelation function $C(t,t_w)=[]_{av}$ a typical aging scenario with a $t/t_w$ scaling is established. Investigating spatial correlations we find an algebraic growth law $\xi(t_w)\sim t_w^{\alpha(T)}$ of the average domain size. The spatial correlation function $G(r,t_w)=[< S_i(t_w)S_{i+r}(t_w)>^2]_{av}$ scales with $r/\xi(t_w)$. The sensitivity of the correlations in the spin glass phase with respect to temperature changes is examined by calculating a time dependent overlap length. In the two dimensional model we examine domain growth with a new method: First we determine the exact ground states of the various samples (of system sizes up to $100\times 100$) and then we calculate the correlations between this state and the states generated during a Monte Carlo simulation.Comment: 38 pages, RevTeX, 14 postscript figure

Spin glass overlap barriers in three and four dimensions

For the Edwards-Anderson Ising spin-glass model in three and four dimensions (3d and 4d) we have performed high statistics Monte Carlo calculations of those free-energy barriers $F^q_B$ which are visible in the probability density $P_J(q)$ of the Parisi overlap parameter $q$. The calculations rely on the recently introduced multi-overlap algorithm. In both dimensions, within the limits of lattice sizes investigated, these barriers are found to be non-self-averaging and the same is true for the autocorrelation times of our algorithm. Further, we present evidence that barriers hidden in $q$ dominate the canonical autocorrelation times.Comment: 20 pages, Latex, 12 Postscript figures, revised version to appear in Phys. Rev.

The Potts Fully Frustrated model: Thermodynamics, percolation and dynamics in 2 dimensions

We consider a Potts model diluted by fully frustrated Ising spins. The model corresponds to a fully frustrated Potts model with variables having an integer absolute value and a sign. This model presents precursor phenomena of a glass transition in the high-temperature region. We show that the onset of these phenomena can be related to a thermodynamic transition. Furthermore this transition can be mapped onto a percolation transition. We numerically study the phase diagram in 2 dimensions (2D) for this model with frustration and {\em without} disorder and we compare it to the phase diagram of $i)$ the model with frustration {\em and} disorder and of $ii)$ the ferromagnetic model. Introducing a parameter that connects the three models, we generalize the exact expression of the ferromagnetic Potts transition temperature in 2D to the other cases. Finally, we estimate the dynamic critical exponents related to the Potts order parameter and to the energy.Comment: 10 pages, 10 figures, new result

Short range ferromagnetism and spin glass state in Y0.7Ca0.3MnO3\mathrm{Y_{0.7}Ca_{0.3}MnO_{3}}

Dynamic magnetic properties of $\mathrm{Y_{0.7}Ca_{0.3}MnO_{3}}$ are reported. The system appears to attain local ferromagnetic order at $T_{\mathrm{SRF}} \approx 70$ K. Below this temperature the low field magnetization becomes history dependent, i.e. the zero field cooled (ZFC) and field cooled (FC) magnetization deviate from each other and closely logarithmic relaxation appears at our experimental time scales (0.3-$10^{4}$ sec). The zero field cooled magnetization has a maximum at $T_{\mathrm{f}}\approx 30$ K, whereas the field cooled magnetization continues to increase, although less sharply, also below this temperature. Surprisingly, the dynamics of the system shows non-equilibrium spin glass (SG) features not only below the maximum in the ZFC magnetization, but also in the temperature region between this maximum and $T_{\mathrm{SRF}}$. The aging and temperature cycling experiments show only quantitative differences in the dynamic behavior above and below the maximum in the ZFC-magnetization; similarly, memory effects are observed in both temperature regions. We attribute the high temperature behavior to the existence of clusters of short range ferromagnetic order below $T_{\mathrm{SRF}}$; the configuration evolves into a conventional spin glass state at temperatures below $T_{\mathrm{f}}$.Comment: REVTeX style; 8 pages, 8 figure

Phenomenological glass model for vibratory granular compaction

A model for weakly excited granular media is derived by combining the free volume argument of Nowak et al. [Phys. Rev. E 57, 1971 (1998)] and the phenomenological model for supercooled liquids of Adam and Gibbs [J. Chem. Phys. 43, 139 (1965)]. This is made possible by relating the granular excitation parameter \Gamma, defined as the peak acceleration of the driving pulse scaled by gravity, to a temperature-like parameter \eta(\Gamma). The resulting master equation is formally identical to that of Bouchaud's trap model for glasses [J. Phys. I 2, 1705 (1992)]. Analytic and simulation results are shown to compare favourably with a range of known experimental behaviour. This includes the logarithmic densification and power spectrum of fluctuations under constant \eta, the annealing curve when \eta is varied cyclically in time, and memory effects observed for a discontinuous shift in \eta. Finally, we discuss the physical interpretation of the model parameters and suggest further experiments for this class of systems.Comment: 2 references added; some figure labels tweaked. To appear in PR

The Karolinska NeuroCOVID study protocol: Neurocognitive impairment, biomarkers and advanced imaging in critical care survivors

Background: This is the study plan of the Karolinska NeuroCOVID study, a study of neurocognitive impairment after severe COVID-19, relating post-intensive care unit (ICU) cognitive and neurological deficits to biofluid markers and MRI. The COVID-19 pandemic has posed enormous health challenges to individuals and health-care systems worldwide. An emerging feature of severe COVID-19 is that of temporary and extended neurocognitive impairment, exhibiting a myriad of symptoms and signs. The causes of this symptomatology have not yet been fully elucidated. Methods: In this study, we aim to investigate patients treated for severe COVID-19 in the ICU, as to describe and relate serum-, plasma- and cerebrospinal fluid-borne molecular and cellular biomarkers of immune activity, coagulopathy, cerebral damage, neuronal inflammation, and degeneration, to the temporal development of structural and functional changes within the brain as evident by serial MRI and extensive cognitive assessments at 3–12 months after ICU discharge. Results: To date, we have performed 51 3-month follow-up MRIs in the ICU survivors. Of these, two patients (~4%) have had incidental findings on brain MRI findings requiring activation of the Incidental Findings Management Plan. Furthermore, the neuropsychological and neurological examinations have so far revealed varying and mixed patterns. Several patients expressed cognitive and/or mental concerns and fatigue, complaints closely related to brain fog. Conclusion: The study goal is to gain a better understanding of the pathological mechanisms and neurological consequences of this new disease, with a special emphasis on neurodegenerative and neuroinflammatory processes, in order to identify targets of intervention and rehabilitation