41 research outputs found
Counterion correlations and attraction between like-charged macromolecules
A simple model is presented for the appearance of attraction between two like
charged polyions inside a polyelectrolyte solution. The polyions are modeled as
rigid cylinders in a continuum dielectric solvent. The strong electrostatic
interactions between the polyions and the counterions results in counterion
condensation. If the two polyions are sufficiently close to each other their
layers of condensed counterions can become correlated resulting in attraction
between the macromolecules. To explore the counterion induced attraction we
calculate the correlation functions for the condensed counterions. It is found
that the correlations are of very short range. For the parameters specific to
the double stranded DNA, the correlations and the attraction appear only when
the surface-to-surface separation is less than 7 /AA.Comment: 6 pages, 8 eps figures, RevTeX with epsfi
From fracture to fragmentation: discrete element modeling -- Complexity of crackling noise and fragmentation phenomena revealed by discrete element simulations
Discrete element modelling (DEM) is one of the most efficient computational
approaches to the fracture processes of heterogeneous materials on mesoscopic
scales. From the dynamics of single crack propagation through the statistics of
crack ensembles to the rapid fragmentation of materials DEM had a substantial
contribution to our understanding over the past decades. Recently, the
combination of DEM with other simulation techniques like Finite Element
Modelling further extended the field of applicability. In this paper we briefly
review the motivations and basic idea behind the DEM approach to cohesive
particulate matter and then we give an overview of on-going developments and
applications of the method focusing on two fields where recent success has been
achieved. We discuss current challenges of this rapidly evolving field and
outline possible future perspectives and debates
Time evolution of the behaviour of Brazilian legislative Representatives using a complex network approach
The follow up of Representative behavior after elections is imperative for a
democratic Representative system, at the very least to punish betrayal with no
re-election. Our goal was to show how to follow Representatives' and how to
show behavior in real situations and observe trends in political crises
including the onset of game changing political instabilities. We used
correlation and correlation distance matrices of Brazilian Representative votes
during four presidential terms. Re-ordering these matrices with Minimal
Spanning Trees displays the dynamical formation of clusters for the sixteen
year period, which includes one Presidential impeachment. The reordered
matrices, colored by correlation strength and by the parties clearly show the
origin of observed clusters and their evolution over time. When large clusters
provide government support cluster breaks, political instability arises, which
could lead to an impeachment, a trend we observed three years before the
Brazilian President was impeached. We believe this method could be applied to
foresee other political storms.Comment: 11 pages, 4 Figure
Distinct DNA methylomes of newborns and centenarians
Human aging cannot be fully understood in terms of the constrained genetic setting. Epigenetic drift is an alternative means of explaining age-associated alterations. To address this issue, we performed whole-genome bisulfite sequencing (WGBS) of newborn and centenarian genomes. The centenarian DNA had a lower DNA methylation content and a reduced correlation in the methylation status of neighboring cytosine--phosphate--guanine (CpGs) throughout the genome in comparison with the more homogeneously methylated newborn DNA. The more hypomethylated CpGs observed in the centenarian DNA compared with the neonate covered all genomic compartments, such as promoters, exonic, intronic, and intergenic regions. For regulatory regions, the most hypomethylated sequences in the centenarian DNA were present mainly at CpG-poor promoters and in tissue-specific genes, whereas a greater level of DNA methylation was observed in CpG island promoters. We extended the study to a larger cohort of newborn and nonagenarian samples using a 450,000 CpG-site DNA methylation microarray that reinforced the observation of more hypomethylated DNA sequences in the advanced age group. WGBS and 450,000 analyses of middle-age individuals demonstrated DNA methylomes in the crossroad between the newborn and the nonagenarian/centenarian groups. Our study constitutes a unique DNA methylation analysis of the extreme points of human life at a single-nucleotide resolution level
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Protective intraoperative ventilation with higher versus lower levels of positive end-expiratory pressure in obese patients (PROBESE): study protocol for a randomized controlled trial
Background: Postoperative pulmonary complications (PPCs) increase the morbidity and mortality of surgery in obese patients. High levels of positive end-expiratory pressure (PEEP) with lung recruitment maneuvers may improve intraoperative respiratory function, but they can also compromise hemodynamics, and the effects on PPCs are uncertain. We hypothesized that intraoperative mechanical ventilation using high PEEP with periodic recruitment maneuvers, as compared with low PEEP without recruitment maneuvers, prevents PPCs in obese patients. Methods/design The PRotective Ventilation with Higher versus Lower PEEP during General Anesthesia for Surgery in OBESE Patients (PROBESE) study is a multicenter, two-arm, international randomized controlled trial. In total, 2013 obese patients with body mass index ≥35 kg/m2 scheduled for at least 2 h of surgery under general anesthesia and at intermediate to high risk for PPCs will be included. Patients are ventilated intraoperatively with a low tidal volume of 7 ml/kg (predicted body weight) and randomly assigned to PEEP of 12 cmH2O with lung recruitment maneuvers (high PEEP) or PEEP of 4 cmH2O without recruitment maneuvers (low PEEP). The occurrence of PPCs will be recorded as collapsed composite of single adverse pulmonary events and represents the primary endpoint. Discussion To our knowledge, the PROBESE trial is the first multicenter, international randomized controlled trial to compare the effects of two different levels of intraoperative PEEP during protective low tidal volume ventilation on PPCs in obese patients. The results of the PROBESE trial will support anesthesiologists in their decision to choose a certain PEEP level during general anesthesia for surgery in obese patients in an attempt to prevent PPCs. Trial registration ClinicalTrials.gov identifier: NCT02148692. Registered on 23 May 2014; last updated 7 June 2016. Electronic supplementary material The online version of this article (doi:10.1186/s13063-017-1929-0) contains supplementary material, which is available to authorized users