165 research outputs found
Dynamics of a polymer test chain in a glass forming matrix: The Hartree Approximation
In this paper the Martin-Siggia-Rose formalism is used to derive a
generalized Rouse equation for a test chain in a matrix which can undergo the
glass transition. It is shown that the surrounding matrix renormalizes the
static properties of the test chain. Furthermore the freezing of the different
Rouse modes is investigated. This yields freezing temperatures which depend
from the Rouse mode index.Comment: to be published in Journal de Physique I
Langevin dynamics of the glass forming polymer melt: fluctuations around the random phase approximation
In this paper the Martin-Siggia-Rose (MSR) functional integral representation
is used for the study of the Langevin dynamics of a polymer melt in terms of
collective variables: mass density and response field density. The resulting
generating functional (GF) takes into account fluctuations around the random
phase approximation (RPA) up to an arbitrary order. The set of equations for
the correlation and response functions is derived. It is generally shown that
for cases whenever the fluctuation-dissipation theorem (FDT) holds we arrive at
equations similar to those derived by Mori-Zwanzig. The case when FDT in the
glassy phase is violated is also qualitatively considered and it is shown that
this results in a smearing out of the ideal glass transition. The memory kernel
is specified for the ideal glass transition as a sum of all water-melon
diagrams. For the Gaussian chain model the explicit expression for the memory
kernel was obtained and discussed in a qualitative link to the mode-coupling
equation.Comment: 30 pages, 5 figure
Dynamics of polymeric manifolds in melts: Hartree approximation
The Martin-Siggia-Rose functional technique and the self-consistent Hartree
approximation is applied to the dynamics of a D-dimensional manifold in a melt
of similar manifolds.The generalized Rouse equation is derived and its static
and dynamic properties are studied. The static upper critical dimension
discriminate between Gaussian and non-Gaussian regimes, whereas its dynamic
counterpart discriminates between Rouse- and renormalized-Rouse behavior. The
dynamic exponents are calculated explicitly. The special case of linear chains
shows agreement with MD- and MC-simulations.Comment: 4 pages,1 figures, accepted by EPJB as a Rapid Not
The Hartree approximation in dynamics of polymeric manifolds in the melt
The Martin-Siggia-Rose (MSR) functional integral technique is applied to the
dynamics of a D - dimensional manifold in a melt of similar manifolds. The
integration over the collective variables of the melt can be simply implemented
in the framework of the dynamical random phase approximation (RPA). The
resulting effective action functional of the test manifold is treated by making
use of the selfconsistent Hartree approximation. As an outcome the generalized
Rouse equation (GRE) of the test manifold is derived and its static and dynamic
properties are studied. It was found that the static upper critical dimension,
, discriminates between Gaussian (or screened) and
non-Gaussian regimes, whereas its dynamical counterpart, , distinguishes between the simple Rouse and the
renormalized Rouse behavior. We have argued that the Rouse mode correlation
function has a stretched exponential form. The subdiffusional exponents for
this regime are calculated explicitly. The special case of linear chains, D=1,
shows good agreement with MD- and MC-simulations.Comment: 35 pages,3 figures, accepted by J.Chem.Phy
Shorter Leukocyte Telomere Length in Relation to Presumed Nonalcoholic Fatty Liver Disease in Mexican-American Men in NHANES 1999-2002.
Leukocyte telomere length is shorter in response to chronic disease processes associated with inflammation such as diabetes mellitus and coronary artery disease. Data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2002 was used to explore the relationship between leukocyte telomere length and presumed NAFLD, as indicated by elevated serum alanine aminotransferase (ALT) levels, obesity, or abdominal obesity. Logistic regression models were used to evaluate the relationship between telomere length and presumed markers of NAFLD adjusting for possible confounders. There was no relationship between elevated ALT levels, abdominal obesity, or obesity and telomere length in adjusted models in NHANES (OR 1.13, 95% CI 0.48-2.65; OR 1.17, 95% CI 0.52-2.62, resp.). Mexican-American men had shorter telomere length in relation to presumed NAFLD (OR 0.07, 95% CI 0.006-0.79) and using different indicators of NAFLD (OR 0.012, 95% CI 0.0006-0.24). Mexican origin with presumed NAFLD had shorter telomere length than men in other population groups. Longitudinal studies are necessary to evaluate the role of telomere length as a potential predictor to assess pathogenesis of NALFD in Mexicans
Collapse or Swelling Dynamics of Homopolymer Rings: Self-consistent Hartree approach
We investigate by the use of the Martin - Siggia - Rose generating functional
technique and the self - consistent Hartree approximation, the dynamics of the
ring homopolymer collapse (swelling) following an instantaneous change into a
poor (good) solvent conditions.The equation of motion for the time dependent
monomer - to - monomer correlation function is systematically derived. It is
argued that for describing of the coarse - graining process (which neglects the
capillary instability and the coalescence of ``pearls'') the Rouse mode
representation is very helpful, so that the resulting equations of motion can
be simply solved numerically. In the case of the collapse this solution is
analyzed in the framework of the hierarchically crumpled fractal picture, with
crumples of successively growing scale along the chain. The presented numerical
results are in line with the corresponding simple scaling argumentation which
in particular shows that the characteristic collapse time of a segment of
length scales as (where is a bare
friction coefficient and is a depth of quench). In contrast to the
collapse the globule swelling can be seen (in the case that topological effects
are neglected) as a homogeneous expansion of the globule interior. The swelling
of each Rouse mode as well as gyration radius is discussed.Comment: 20 pages, 7 figures, submitted to Phys. Rev.
Genetic vulnerability to diabetes and obesity: does education offset the risk?
The prevalence of type 2 diabetes (T2D) and obesity has recently increased dramatically. These common diseases are likely to arise from the interaction of multiple genetic, socio-demographic and environmental risk factors. While previous research has found genetic risk and education to be strong predictors of these diseases, few studies to date have examined their joint effects. This study investigates whether education modifies the association between genetic background and risk for type 2 diabetes (T2D) and obesity. Using data from non-Hispanic Whites in the Health and Retirement Study (HRS, n = 8398), we tested whether education modifies genetic risk for obesity and T2D, offsetting genetic effects; whether this effect is larger for individuals who have high risk for other (unobserved) reasons, i.e., at higher quantiles of HbA1c and BMI; and whether effects differ by gender. We measured T2D risk using Hemoglobin A1c (HbA1c) level, and obesity risk using body-mass index (BMI). We constructed separate genetic risk scores (GRS) for obesity and diabetes respectively based on the most current available information on the single nucleotide polymorphism (SNPs) confirmed as genome-wide significant predictors for BMI (29 SNPs) and diabetes risk (39 SNPs). Linear regression models with years of schooling indicate that the effect of genetic risk on HbA1c is smaller among people with more years of schooling and larger among those with less than a high school (HS) degree compared to HS degree-holders. Quantile regression models show that the GRS × education effect systematically increased along the HbA1c outcome distribution; for example the GRS × years of education interaction coefficient was −0.01 (95% CI = −0.03, 0.00) at the 10th percentile compared to −0.03 (95% CI = −0.07, 0.00) at the 90th percentile. These results suggest that education may be an important socioeconomic source of heterogeneity in responses to genetic vulnerability to T2D
Shorter Leukocyte Telomere Length in Relation to Presumed Nonalcoholic Fatty Liver Disease in Mexican-American Men in NHANES 1999–2002
Leukocyte telomere length is shorter in response to chronic disease processes associated with inflammation such as diabetes mellitus and coronary artery disease. Data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2002 was used to explore the relationship between leukocyte telomere length and presumed NAFLD, as indicated by elevated serum alanine aminotransferase (ALT) levels, obesity, or abdominal obesity. Logistic regression models were used to evaluate the relationship between telomere length and presumed markers of NAFLD adjusting for possible confounders. There was no relationship between elevated ALT levels, abdominal obesity, or obesity and telomere length in adjusted models in NHANES (OR 1.13, 95% CI 0.48–2.65; OR 1.17, 95% CI 0.52–2.62, resp.). Mexican-American men had shorter telomere length in relation to presumed NAFLD (OR 0.07, 95% CI 0.006–0.79) and using different indicators of NAFLD (OR 0.012, 95% CI 0.0006–0.24). Mexican origin with presumed NAFLD had shorter telomere length than men in other population groups. Longitudinal studies are necessary to evaluate the role of telomere length as a potential predictor to assess pathogenesis of NALFD in Mexicans
Report on the Joint Workshop on the Relations between Health Inequalities, Ageing and Multimorbidity, Iceland, May 3-4, 2023
This paper is a summary of key presentations from a workshop in Iceland on May 3– 4, 2023 arranged by Aarhus University and with participation of the below-mentioned scientists.Below you will find the key messages from the presentations made by:Professor Jan Vandenbroucke, Department of Clinical Epidemiology, Aarhus University, Emeritus Professor, Leiden University; Honorary Professor, London School of Hygiene & Tropical Medicine, UKProfessor, Chair Henrik Toft Sørensen, Department of Clinical Epidemiology, Aarhus University and Aarhus University Hospital, DenmarkProfessor David H. Rehkopf, Director, the Stanford Center for Population Health Sciences, Stanford University, CA., USProfessor Jaimie Gradus, Department of Epidemiology, School of Public Health, Boston University, Boston, Massachusetts, USProfessor Johan Mackenbach, Emeritus Professor, Department of Public Health, Erasmus University Rotterdam, HollandProfessor, Chair M Maria Glymour, Department of Epidemiology, Boston University School of Public Health, Boston University, Boston, Massachusetts, USProfessor, Dean Sandro Galea, School of Public Health, Boston University, Boston, Massachusetts, USProfessor Victor W. Henderson, Departments of Epidemiology & Population Health and of Neurology & Neurological Sciences, Stanford University, Stanford, CA, US; Department of Clinical Epidemiology, Aarhus University, Aarhus, D
Sex differences in epigenetic age in Mediterranean high longevity regions
Sex differences in aging manifest in disparities in disease prevalence, physical health, and lifespan, where women tend to have greater longevity relative to men. However, in the Mediterranean Blue Zones of Sardinia (Italy) and Ikaria (Greece) are regions of centenarian abundance, male-female centenarian ratios are approximately one, diverging from the typical trend and making these useful regions in which to study sex differences of the oldest old. Additionally, these regions can be investigated as examples of healthy aging relative to other populations. DNA methylation (DNAm)-based predictors have been developed to assess various health biomarkers, including biological age, Pace of Aging, serum interleukin-6 (IL-6), and telomere length. Epigenetic clocks are biological age predictors whose deviation from chronological age has been indicative of relative health differences between individuals, making these useful tools for interrogating these differences in aging. We assessed sex differences between the Horvath, Hannum, GrimAge, PhenoAge, Skin and Blood, and Pace of Aging predictors from individuals in two Mediterranean Blue Zones and found that men displayed positive epigenetic age acceleration (EAA) compared to women according to all clocks, with significantly greater rates according to GrimAge (β = 3.55; p = 1.22 × 10-12), Horvath (β = 1.07; p = 0.00378) and the Pace of Aging (β = 0.0344; p = 1.77 × 10-08). Other DNAm-based biomarkers findings indicated that men had lower DNAm-predicted serum IL-6 scores (β = -0.00301, p = 2.84 × 10-12), while women displayed higher DNAm-predicted proportions of regulatory T cells than men from the Blue Zone (p = 0.0150, 95% Confidence Interval [0.00131, 0.0117], Cohen's d = 0.517). All clocks showed better correlations with chronological age in women from the Blue Zones than men, but all clocks showed large mean absolute errors (MAE >30 years) in both sexes, except for PhenoAge (MAE <5 years). Thus, despite their equal survival to older ages in these Mediterranean Blue Zones, men in these regions remain biologically older by most measured DNAm-derived metrics than women, with the exception of the IL-6 score and proportion of regulatory T cells
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