Critical behavior of a fluid in a disordered porous matrix: An Ornstein-Zernike approach

Using a liquid-state approach based on Ornstein-Zernike equations, we study the behavior of a fluid inside a porous disordered matrix near the liquid-gas critical point.The results obtained within various standard approximation schemes such as lowest-order $\gamma$-ordering and the mean-spherical approximation suggest that the critical behavior is closely related to that of the random-field Ising model (RFIM).Comment: 10 pages, revtex, to appear in Physical Review Letter

New algorithm and results for the three-dimensional random field Ising Model

The random field Ising model with Gaussian disorder is studied using a new Monte Carlo algorithm. The algorithm combines the advantanges of the replica exchange method and the two-replica cluster method and is much more efficient than the Metropolis algorithm for some disorder realizations. Three-dimensional sytems of size $24^3$ are studied. Each realization of disorder is simulated at a value of temperature and uniform field that is adjusted to the phase transition region for that disorder realization. Energy and magnetization distributions show large variations from one realization of disorder to another. For some realizations of disorder there are three well separated peaks in the magnetization distribution and two well separated peaks in the energy distribution suggesting a first-order transition.Comment: 24 pages, 23 figure

Синдром старческой астении у пациентов с заболеваниями респираторной системы

Respiratory diseases such as asthma and chronic obstructive pulmonary disease are especially prevalent in elderly people and have become a significant problem for healthcare due to ageing of population. Frailty syndrome (FS) is a geriatric syndrome characterized by an age-associated declines in physiologic reserve and functions of multiple systems, including respiratory system. This syndrome leads to increased vulnerability of the elderly.The aim of the study is to review the available data on modern understanding of FS, pathophysiological changes in the respiratory system associated with aging, the prevalence of FS, and its potential underlying mechanisms in elderly patients with respiratory diseases.Conclusion. FS is strongly associated with respiratory diseases. On one hand, these pathophysiological processes are inherent in elderly patients. On the other hand, the condition itself causes additional changes that enhance the aging process. Undoubtedly, their association and the influence of FS on the course and outcomes of the respiratory disease should be studied to improve the prognosis of elderly patients. Early recognition of FS in patients with respiratory diseases will help prevent or delay decline in physiologic reserve and functions of multiple systems and lower the disability and mortality rates. Comprehensive assessment of “frail” patients can assist in developing a better risk stratification and provide a personalized approach to managing these risks, as well as improve the patient outcomes.По мере старения населения заболевания легких, такие как бронхиальная астма, хроническая обструктивная болезнь легких – одни из наиболее распространенных у пожилых людей, представляют собой важную проблему для системы здравоохранения. Синдром старческой астении (ССА) – гериатрический синдром, который характеризуется возраст-ассоциированным снижением физиологического резерва и функций многих систем, в т. ч. респираторной, приводит к повышенной уязвимости организма пожилого человека.Целью работы явился обзор исследований, при проведении которых затрагивались вопросы современного представления о ССА, патофизиологических изменений респираторной систему у пожилых, распространенности, а также возможных механизмах развития ССА у пожилых пациентов с заболеваниями респираторной системы.Заключение. ССА и заболевания респираторной системы тесно связаны между собой. С одной стороны, эти патофизиологические процессы закономерно присутствуют у пожилых людей, с другой – это сама патология, которая вносит дополнительные изменения, усиливающих процесс старения. Несомненно, изучение вопроса взаимодействия, а также влияния ССА на течение и исходы заболевания имеет огромное значение для улучшения прогноза у пожилых пациентов. Раннее распознавание ССА у пациентов с патологией респираторной системы поможет предотвратить или отсрочить ухудшение функциональности, инвалидности и смерти. При оценке степени «слабости» у пациентов могут улучшиться стратификация рисков и персонифицированный подход к управлению данными рисками, а также результаты лечения

Power-law correlations and orientational glass in random-field Heisenberg models

Monte Carlo simulations have been used to study a discretized Heisenberg ferromagnet (FM) in a random field on simple cubic lattices. The spin variable on each site is chosen from the twelve [110] directions. The random field has infinite strength and a random direction on a fraction x of the sites of the lattice, and is zero on the remaining sites. For x = 0 there are two phase transitions. At low temperatures there is a [110] FM phase, and at intermediate temperature there is a [111] FM phase. For x > 0 there is an intermediate phase between the paramagnet and the ferromagnet, which is characterized by a |k|^(-3) decay of two-spin correlations, but no true FM order. The [111] FM phase becomes unstable at a small value of x. At x = 1/8 the [110] FM phase has disappeared, but the power-law correlated phase survives.Comment: 8 pages, 12 Postscript figure

Equilibrium random-field Ising critical scattering in the antiferromagnet Fe(0.93)Zn(0.07)F2

It has long been believed that equilibrium random-field Ising model (RFIM) critical scattering studies are not feasible in dilute antiferromagnets close to and below Tc(H) because of severe non-equilibrium effects. The high magnetic concentration Ising antiferromagnet Fe(0.93)Zn(0.07)F2, however, does provide equilibrium behavior. We have employed scaling techniques to extract the universal equilibrium scattering line shape, critical exponents nu = 0.87 +- 0.07 and eta = 0.20 +- 0.05, and amplitude ratios of this RFIM system.Comment: 4 pages, 1 figure, minor revision

Scaling and self-averaging in the three-dimensional random-field Ising model

We investigate, by means of extensive Monte Carlo simulations, the magnetic critical behavior of the three-dimensional bimodal random-field Ising model at the strong disorder regime. We present results in favor of the two-exponent scaling scenario, $\bar{\eta}=2\eta$, where $\eta$ and $\bar{\eta}$ are the critical exponents describing the power-law decay of the connected and disconnected correlation functions and we illustrate, using various finite-size measures and properly defined noise to signal ratios, the strong violation of self-averaging of the model in the ordered phase.Comment: 8 pages, 6 figures, to be published in Eur. Phys. J.

Specific-Heat Exponent of Random-Field Systems via Ground-State Calculations

Exact ground states of three-dimensional random field Ising magnets (RFIM) with Gaussian distribution of the disorder are calculated using graph-theoretical algorithms. Systems for different strengths h of the random fields and sizes up to N=96^3 are considered. By numerically differentiating the bond-energy with respect to h a specific-heat like quantity is obtained, which does not appear to diverge at the critical point but rather exhibits a cusp. We also consider the effect of a small uniform magnetic field, which allows us to calculate the T=0 susceptibility. From a finite-size scaling analysis, we obtain the critical exponents \nu=1.32(7), \alpha=-0.63(7), \eta=0.50(3) and find that the critical strength of the random field is h_c=2.28(1). We discuss the significance of the result that \alpha appears to be strongly negative.Comment: 9 pages, 9 figures, 1 table, revtex revised version, slightly extende

Anderson-Mott transition as a quantum glass problem

We combine a recent mapping of the Anderson-Mott metal-insulator transition on a random-field problem with scaling concepts for random-field magnets to argue that disordered electrons near an Anderson-Mott transition show glass-like behavior. We first discuss attempts to interpret experimental results in terms of a conventional scaling picture, and argue that some of the difficulties encountered point towards a glassy nature of the electrons. We then develop a general scaling theory for a quantum glass, and discuss critical properties of both thermodynamic and transport variables in terms of it. Our most important conclusions are that for a correct interpretation of experiments one must distinguish between self-averaging and non-self averaging observables, and that dynamical or temperature scaling is not of power-law type but rather activated, i.e. given by a generalized Vogel-Fulcher law. Recent mutually contradicting experimental results on Si:P are discussed in the light of this, and new experiments are proposed to test the predictions of our quantum glass scaling theory.Comment: 25pp, REVTeX, 5 ps figs, final version as publishe

Tricritical Points in the Sherrington-Kirkpatrick Model in the Presence of Discrete Random Fields

The infinite-range-interaction Ising spin glass is considered in the presence of an external random magnetic field following a trimodal (three-peak) distribution. The model is studied through the replica method and phase diagrams are obtained within the replica-symmetry approximation. It is shown that the border of the ferromagnetic phase may present first-order phase transitions, as well as tricritical points at finite temperatures. Analogous to what happens for the Ising ferromagnet under a trimodal random field, it is verified that the first-order phase transitions are directly related to the dilution in the fields (represented by $p_{0}$). The ferromagnetic boundary at zero temperature also exhibits an interesting behavior: for $0<p_{0}<p_{0}^{*} \approx 0.30856$, a single tricritical point occurs, whereas if $p_{0}>p_{0}^{*}$ the critical frontier is completely continuous; however, for $p_{0}=p_{0}^{*}$, a fourth-order critical point appears. The stability analysis of the replica-symmetric solution is performed and the regions of validity of such a solution are identified; in particular, the Almeida-Thouless line in the plane field versus temperature is shown to depend on the weight $p_{0}$.Comment: 23pages, 7 ps figure