Fluctuations in glassy systems

We summarize a theoretical framework based on global time-reparametrization invariance that explains the origin of dynamic fluctuations in glassy systems. We introduce the main ideas without getting into much technical details. We describe a number of consequences arising from this scenario that can be tested numerically and experimentally distinguishing those that can also be explained by other mechanisms from the ones that we believe, are special to our proposal. We support our claims by presenting some numerical checks performed on the 3d Edwards-Anderson spin-glass. Finally, we discuss up to which extent these ideas apply to super-cooled liquids that have been studied in much more detail up to present.Comment: 33 pages, 7 figs, contribution to JSTAT special issue `Principles of Dynamical Systems' work-shop at Newton Institute, Univ. of Cambridge, U

Sources of academic stress among Iranian adolescents: a multilevel study from Qazvin City, Iran

Background: Academic stress can cause mental and physical problems and affect adolescents’ healthy development. This study aimed to estimate academic stress and explore its sources at the individual- and school levels among school-going adolescents in the city of Qazvin, Iran. Results: This cross-sectional study used a stratified cluster sampling to recruit 1724 students aged 12–19 years from 53 schools in Qazvin City. Data were collected using a validated self-administered questionnaire. The mean academic stress score was 45.7 (95% CI 45.2, 46.3). The stress level was statistically higher among older 47.5 (95% CI 46.7, 48.3) than younger 44.1 (95% CI 43.4, 44.9) adolescents. The main academic stressors included: future uncertainty 69.7 (95% CI 68.8, 70.7), academic competition 58.5 (95% CI 57.3, 59.6), and interaction with teachers 56.1 (95% CI 55.3, 56.9). Gender, educational period, school type, family socioeconomic status, and father’s education were associated with academic stress. Conclusions: We conducted a multilevel study using a random sample of male and female students in the city of Qazvin, Iran. Results indicated moderate levels of stress among Iranian adolescents. The academic stress was associated with several individual and school-level variables. Students and their families and teachers need education on stress prevention methods and coping mechanisms. Future research should focus on developing and testing multilevel policies and interventions to improve students’ mental health and academic performance. Keywords: Academic stress, Adolescence, Students, Multilevel analysis, Ira

Sources of academic stress among Iranian adolescents: a multilevel study from Qazvin City, Iran

Background: Academic stress can cause mental and physical problems and affect adolescents’ healthy development. This study aimed to estimate academic stress and explore its sources at the individual- and school levels among school-going adolescents in the city of Qazvin, Iran. Results: This cross-sectional study used a stratified cluster sampling to recruit 1724 students aged 12–19 years from 53 schools in Qazvin City. Data were collected using a validated self-administered questionnaire. The mean academic stress score was 45.7 (95% CI 45.2, 46.3). The stress level was statistically higher among older 47.5 (95% CI 46.7, 48.3) than younger 44.1 (95% CI 43.4, 44.9) adolescents. The main academic stressors included: future uncertainty 69.7 (95% CI 68.8, 70.7), academic competition 58.5 (95% CI 57.3, 59.6), and interaction with teachers 56.1 (95% CI 55.3, 56.9). Gender, educational period, school type, family socioeconomic status, and father’s education were associated with academic stress. Conclusions: We conducted a multilevel study using a random sample of male and female students in the city of Qazvin, Iran. Results indicated moderate levels of stress among Iranian adolescents. The academic stress was associated with several individual and school-level variables. Students and their families and teachers need education on stress prevention methods and coping mechanisms. Future research should focus on developing and testing multilevel policies and interventions to improve students’ mental health and academic performance. Keywords: Academic stress, Adolescence, Students, Multilevel analysis, Ira

Growing dynamical length, scaling and heterogeneities in the 3d Edwards-Anderson model

We study numerically spatio-temporal fluctuations during the out-of-equilibrium relaxation of the three-dimensional Edwards-Anderson model. We focus on two issues. (1) The evolution of a growing dynamical length scale in the glassy phase of the model, and the consequent collapse of the distribution of local coarse-grained correlations measured at different pairs of times on a single function using {\it two} scaling parameters, the value of the global correlation at the measuring times and the ratio of the coarse graining length to the dynamical length scale (in the thermodynamic limit). (2) The `triangular' relation between coarse-grained local correlations at three pairs of times taken from the ordered instants $t_3 \leq t_2 \leq t_1$. Property (1) is consistent with the conjecture that the development of time-reparametrization invariance asymptotically is responsible for the main dynamic fluctuations in aging glassy systems as well as with other mechanisms proposed in the literature. Property (2), we stress, is a much stronger test of the relevance of the time-reparametrization invariance scenario.Comment: 24 pages, 12 fig

Fluctuations of two-time quantities and time-reparametrization invariance in spin-glasses

This article is a contribution to the understanding of fluctuations in the out of equilibrium dynamics of glassy systems. By extending theoretical ideas based on the assumption that time-reparametrization invariance develops asymptotically we deduce the scaling properties of diverse high-order correlation functions. We examine these predictions with numerical tests in a standard glassy model, the 3d Edwards-Anderson spin-glass, and in a system where time-reparametrization invariance is not expected to hold, the 2d ferromagnetic Ising model, both at low temperatures. Our results enlighten a qualitative difference between the fluctuation properties of the two models and show that scaling properties conform to the time-reparametrization invariance scenario in the former but not in the latter.Comment: 17 pages, 5 figure

Scaling and super-universality in the coarsening dynamics of the 3d random field Ising model

We study the coarsening dynamics of the three-dimensional random field Ising model using Monte Carlo numerical simulations. We test the dynamic scaling and super-scaling properties of global and local two-time observables. We treat in parallel the three-dimensional Edward-Anderson spin-glass and we recall results on Lennard-Jones mixtures and colloidal suspensions to highlight the common and different out of equilibrium properties of these glassy systems.Comment: 18 pages, 21 figure

Fluctuations and effective temperatures in coarsening

We study dynamic fluctuations in non-disordered finite dimensional ferromagnetic systems quenched to the critical point and the low-temperature phase. We investigate the fluctuations of two two-time quantities, called $\chi$ and $C$, the averages of which %$$,$$ yield the self linear response and correlation function. We introduce a restricted average of the $\chi$'s, summing over all configurations with a given value of $C$. We find that the restricted average $_C$ obeys a scaling form, and that the slope of the scaling function approaches the universal value $X_\infty$ of the limiting effective temperature in the long-time limit and for $C\to 0$. Our results tend to confirm the expectation that time-reparametrization invariance is not realized in coarsening systems at criticality. Finally, we discuss possible experimental tests of our proposal.Comment: 17 pages, 9 figure

Insight into blood pressure targets for universal coverage of hypertension services in Iran: the 2017 ACC/AHA versus JNC 8 hypertension guidelines

BACKGROUND: We compared the prevalence, awareness, treatment, and control of hypertension in Iran based on two hypertension guidelines; the 2017 ACC/AHA -with an aggressive blood pressure target of 130/80 mmHg- and the commonly used JNC8 guideline cut-off of 140/90 mmHg. We shed light on the implications of the 2017 ACC/AHA for population subgroups and high-risk individuals who were eligible for non-pharmacologic and pharmacologic therapies. METHODS: Data was obtained from the Iran national STEPS 2016 study. Participants included 27,738 adults aged ≥25 years as a representative sample of Iranians. Regression models of survey design were used to examine the determinants of prevalence, awareness, treatment, and control of hypertension. RESULTS: The prevalence of hypertension based on JNC8 was 29.9% (95% CI: 29.2-30.6), which soared to 53.7% (52.9-54.4) based on the 2017 ACC/AHA. The percentage of awareness, treatment, and control were 59.2% (58.0-60.3), 80.2% (78.9-81.4), and 39.1% (37.4-40.7) based on JNC8, which dropped to 37.1% (36.2-38.0), 71.3% (69.9-72.7), and 19.6% (18.3-21.0), respectively, by applying the 2017 ACC/AHA. Based on the new guideline, adults aged 25-34 years had the largest increase in prevalence (from 7.3 to 30.7%). They also had the lowest awareness and treatment rate, contrary to the highest control rate (36.5%) between age groups. Compared with JNC8, based on the 2017 ACC/AHA, 24, 15, 17, and 11% more individuals with dyslipidaemia, high triglycerides, diabetes, and cardiovascular disease events, respectively, fell into the hypertensive category. Yet, based on the 2017 ACC/AHA, 68.2% of individuals falling into the hypertensive category were eligible for receiving pharmacologic therapy (versus 95.7% in JNC8). LDL cholesterol< 130 mg/dL, sufficient physical activity (Metabolic Equivalents≥600/week), and Body Mass Index were found to change blood pressure by - 3.56(- 4.38, - 2.74), - 2.04(- 2.58, - 1.50), and 0.48(0.42, 0.53) mmHg, respectively. CONCLUSIONS: Switching from JNC8 to 2017 ACC/AHA sharply increased the prevalence and drastically decreased the awareness, treatment, and control in Iran. Based on the 2017 ACC/AHA, more young adults and those with chronic comorbidities fell into the hypertensive category; these individuals might benefit from earlier interventions such as lifestyle modifications. The low control rate among individuals receiving treatment warrants a critical review of hypertension services

National and sub-national burden of chronic diseases attributable to lifestyle risk factors in Iran 1990-2013; study protocol

Background: Non-communicable diseases, as the major public health problem, are caused by different risk factors. The main leading lifestyle risk factors for most diseases burden in Iran are unhealthy diet, physical inactivity, and smoking. The aim of this study is to provide data collection and methodology processes for estimating the trends of exposures to the selected lifestyle risk factors and their attributed burden at national and sub-national levels. Methods: Systematic review will be performed through PubMed/MEDLINE, Scopus and ISI/Web of Science as well as Iranian databases such as IranMedex, Irandoc and Scientific Information Database (SID). In addition, hand searching of unpublished data sources will be used to identify relevant population-based studies. The searched studies will be included only if it is reasonably population-based and representative, and exposure data has been reported or could be plausibly obtained from the study. For risk factors with no surveys identified, other sources of potential data will be considered. The target population is healthy Iranian adult population living within Iran from 1990 to 2013. Other data sources include national censuses, national registration systems, and national and sub-national surveys. Spatio-temporal Bayesian hierarchical model and Bayesian multilevel autoregressive model will be used to overcome the problem of data gaps in provinces, and in some age or sex groups or in urban/rural areas. The problem of misaligned areal units will be also addressed in these models. Conclusion: National and sub-national assessment of major lifestyle risk factors such as unhealthy diet, physical inactivity, and smoking is necessary for priority setting and policy making in different regions of Iran

Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks, 1990-2015: a systematic analysis for the Global Burden of Disease Study 2015

SummaryBackground The Global Burden of Diseases, Injuries, and Risk Factors Study 2015 provides an up-to-date synthesis of the evidence for risk factor exposure and the attributable burden of disease. By providing national and subnational assessments spanning the past 25 years, this study can inform debates on the importance of addressing risks in context. Methods We used the comparative risk assessment framework developed for previous iterations of the Global Burden of Disease Study to estimate attributable deaths, disability-adjusted life-years (DALYs), and trends in exposure by age group, sex, year, and geography for 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks from 1990 to 2015. This study included 388 risk-outcome pairs that met World Cancer Research Fund-defined criteria for convincing or probable evidence. We extracted relative risk and exposure estimates from randomised controlled trials, cohorts, pooled cohorts, household surveys, census data, satellite data, and other sources. We used statistical models to pool data, adjust for bias, and incorporate covariates. We developed a metric that allows comparisons of exposure across risk factors—the summary exposure value. Using the counterfactual scenario of theoretical minimum risk level, we estimated the portion of deaths and DALYs that could be attributed to a given risk. We decomposed trends in attributable burden into contributions from population growth, population age structure, risk exposure, and risk-deleted cause-specific DALY rates. We characterised risk exposure in relation to a Socio-demographic Index (SDI). Findings Between 1990 and 2015, global exposure to unsafe sanitation, household air pollution, childhood underweight, childhood stunting, and smoking each decreased by more than 25%. Global exposure for several occupational risks, high body-mass index (BMI), and drug use increased by more than 25% over the same period. All risks jointly evaluated in 2015 accounted for 57·8% (95% CI 56·6–58·8) of global deaths and 41·2% (39·8–42·8) of DALYs. In 2015, the ten largest contributors to global DALYs among Level 3 risks were high systolic blood pressure (211·8 million [192·7 million to 231·1 million] global DALYs), smoking (148·6 million [134·2 million to 163·1 million]), high fasting plasma glucose (143·1 million [125·1 million to 163·5 million]), high BMI (120·1 million [83·8 million to 158·4 million]), childhood undernutrition (113·3 million [103·9 million to 123·4 million]), ambient particulate matter (103·1 million [90·8 million to 115·1 million]), high total cholesterol (88·7 million [74·6 million to 105·7 million]), household air pollution (85·6 million [66·7 million to 106·1 million]), alcohol use (85·0 million [77·2 million to 93·0 million]), and diets high in sodium (83·0 million [49·3 million to 127·5 million]). From 1990 to 2015, attributable DALYs declined for micronutrient deficiencies, childhood undernutrition, unsafe sanitation and water, and household air pollution; reductions in risk-deleted DALY rates rather than reductions in exposure drove these declines. Rising exposure contributed to notable increases in attributable DALYs from high BMI, high fasting plasma glucose, occupational carcinogens, and drug use. Environmental risks and childhood undernutrition declined steadily with SDI; low physical activity, high BMI, and high fasting plasma glucose increased with SDI. In 119 countries, metabolic risks, such as high BMI and fasting plasma glucose, contributed the most attributable DALYs in 2015. Regionally, smoking still ranked among the leading five risk factors for attributable DALYs in 109 countries; childhood underweight and unsafe sex remained primary drivers of early death and disability in much of sub-Saharan Africa. Interpretation Declines in some key environmental risks have contributed to declines in critical infectious diseases. Some risks appear to be invariant to SDI. Increasing risks, including high BMI, high fasting plasma glucose, drug use, and some occupational exposures, contribute to rising burden from some conditions, but also provide opportunities for intervention. Some highly preventable risks, such as smoking, remain major causes of attributable DALYs, even as exposure is declining. Public policy makers need to pay attention to the risks that are increasingly major contributors to global burden. Funding Bill & Melinda Gates Foundation