1,047 research outputs found
Like-Charge Colloid-Polyelectrolyte Complexation
We investigate the complexation of a highly charged sphere with a long
flexible polyelectrolyte, \textit{both negatively charged} in salt free
environment. Electroneutrality is insured by the presence of divalent
counterions. Using molecular dynamics (MD) within the framework of the
primitive model, we consider different Coulomb coupling regimes. At strong
Coulomb coupling we find that the adsorbed chain is always confined to the
colloidal surface but forms different conformations that depend on the linear
charge density of the chain. A mechanism involving the polyelectrolyte
\textit{overcharging} is proposed to explain these structures. At intermediate
Coulomb coupling, the chain conformation starts to become three-dimensional,
and we observe multilayering of the highly charged chain while for lower charge
density the chain wraps around the colloid. At weak Coulomb coupling,
corresponding to an aqueous solvent, we still find like-charge complexation. In
this latter case the chain conformation exhibits loops.Comment: 18 pages, 13 (main) eps figures, RevTeX4, submitted to J. Chem. Phy
Effect of colloidal charge discretization in the primitive model
The effect of fixed discrete colloidal charges in the primitive model is
investigated for spherical macroions. Instead of considering a central bare
charge, as it is traditionally done, we distribute \textit{discrete} charges
randomly on the sphere. We use molecular dynamics simulations to study this
effect on various properties such as overcharging, counterion distribution and
diffusion. In the vicinity of the colloid surface the electrostatic potential
may considerably differ from the one obtained with a central charge. In the
strong Coulomb coupling, we showed that the colloidal charge discretization
qualitatively influences the counterion distribution and leads to a strong
colloidal charge-counterion pair association. However, we found that
\textit{charge inversion} still persists even if strong pair association is
observed.Comment: 16 pages, 16 ps figures, REVTEX, accepted for publication in EPJ
Polyelectrolyte Multilayering on a Charged Sphere
The adsorption of highly \textit{oppositely} charged flexible
polyelectrolytes onto a charged spherical surface is investigated by means of
Monte Carlo simulations in a fashion which resembles the layer-by-layer
deposition technique introduced by Decher. Electroneutrality is insured at each
step by the presence of monovalent counterions (anions and cations). We study
in detail the structure of the \textit{equilibrium} complex. Our investigations
of the first few layer formations strongly suggest that multilayering in
spherical geometry is not possible as an equilibrium process with purely
electrostatic interactions. We especially focus on the influence of specific
(non-electrostatic) short range attractive interactions (e.g., Van der Waals)
on the stability of the multilayers.Comment: 24 Pages - 15 (main) Figs - RevTeX 4 - published versio
Tendon collagen synthesis declines with immobilization in elderly humans:no effect of anti-inflammatory medication
Nonsteroidal anti-inflammatory drugs (NSAIDs) are used as pain killers during periods of unloading caused by traumatic occurrences or diseases. However, it is unknown how tendon protein turnover and mechanical properties respond to unloading and subsequent reloading in elderly humans, and whether NSAID treatment would affect the tendon adaptations during such periods. Thus we studied human patellar tendon protein synthesis and mechanical properties during immobilization and subsequent rehabilitating resistance training and the influence of NSAIDs upon these parameters. Nineteen men (range 60â80 yr) were randomly assigned to NSAIDs (ibuprofen 1,200 mg/day; Ibu) or placebo (Plc). One lower limb was immobilized in a cast for 2 wk and retrained for 6 wk. Tendon collagen protein synthesis, mechanical properties, size, expression of genes related to collagen turnover and remodeling, and signal intensity (from magnetic resonance imaging) were investigated. Tendon collagen synthesis decreased ( P < 0.001), whereas tendon mechanical properties and size were generally unchanged with immobilization, and NSAIDs did not influence this. Matrix metalloproteinase-2 mRNA tended to increase ( P < 0.1) after immobilization in both groups, whereas scleraxis mRNA decreased with inactivity in the Plc group only ( P < 0.05). In elderly human tendons, collagen protein synthesis decreased after 2 wk of immobilization, whereas tendon stiffness and modulus were only marginally reduced, and NSAIDs had no influence upon this. This indicates an importance of mechanical loading for maintenance of tendon collagen turnover. However, reduced collagen production induced by short-term unloading may only marginally affect tendon mechanical properties in elderly individuals.NEW & NOTEWORTHY In elderly humans, 2 wk of inactivity reduces tendon collagen protein synthesis, while tendon stiffness and modulus are only marginally reduced, and NSAID treatment does not affect this. This indicates that mechanical loading is important for maintenance of tendon collagen turnover and that changes in collagen turnover induced by short-term immobilization may only have minor impact on the internal structures that are essential for mechanical properties in elderly tendons.</jats:p
Cerebellar mutism syndrome in children with brain tumours of the posterior fossa
Background: Central nervous system tumours constitute 25% of all childhood cancers; more than half are located in the posterior fossa and surgery is usually part of therapy. One of the most disabling late effects of posterior fossa tumour surgery is the cerebellar mutism syndrome (CMS) which has been reported in up to 39% of the patients but the exact incidence is uncertain since milder cases may be unrecognized. Recovery is usually incomplete. Reported risk factors are tumour type, midline location and brainstem involvement, but the exact aetiology, surgical and other risk factors, the clinical course and strategies for prevention and treatment are yet to be determined. Methods: This observational, prospective, multicentre study will include 500 children with posterior fossa tumours. It opened late 2014 with participation from 20 Nordic and Baltic centres. From 2016, five British centres and four Dutch centres will join with a total annual accrual of 130 patients. Three other major European centres are invited to join from 2016/17. Follow-up will run for 12 months after inclusion of the last patient. All patients are treated according to local practice. Clinical data are collected through standardized online registration at pre-determined time points pre- and postoperatively. Neurological status and speech functions are examined pre- operatively and postoperatively at 1-4 weeks, 2 and 12 months. Pre- and postoperative speech samples are recorded and analysed. Imaging will be reviewed centrally. Pathology is classified according to the 2007 WHO system. Germline DNA will be collected from all patients for associations between CMS characteristics and host genome variants including pathway profiles. Discussion: Through prospective and detailed collection of information on 1) differences in incidence and clinical course of CMS for different patient and tumour characteristics, 2) standardized surgical data and their association with CMS, 3) diversities and results of other therapeutic interventions, and 4) the role of host genome variants, we aim to achieve a better understanding of risk factors for and the clinical course of CMS - with the ultimate goal of defining strategies for prevention and treatment of this severely disabling condition.Peer reviewe
Radio Astronomy
Contains summary of research and reports on seven research projects.National Science Foundation (Grant AST82-14296)National Aeronautics and Space Administration (Grant NAGW-373)National Aeronautics and Space Administration (Contract NAS5-28410)U.S. Navy - Office of Naval Research (Contract N00014-84-C-2082)M.I.T. Sloan Fund for Basic ResearchNational Oceanic and Atmospheric Administration (Grant 04-8-M01-1)National Aeronautics and Space Administration (Grant NAG5-10)Defense Advanced Research Project Agency (Contract MDA 903-84-K-0297
Inflammation Aggravates Disease Severity in Marfan Syndrome Patients
BACKGROUND: Marfan syndrome (MFS) is a pleiotropic genetic disorder with major features in cardiovascular, ocular and skeletal systems, associated with large clinical variability. Numerous studies reveal an involvement of TGF-beta signaling. However, the contribution of tissue inflammation is not addressed so far. METHODOLOGY/PRINCIPAL FINDINGS: Here we showed that both TGF-beta and inflammation are up-regulated in patients with MFS. We analyzed transcriptome-wide gene expression in 55 MFS patients using Affymetrix Human Exon 1.0 ST Array and levels of TGF-beta and various cytokines in their plasma. Within our MFS population, increased plasma levels of TGF-beta were found especially in MFS patients with aortic root dilatation (124 pg/ml), when compared to MFS patients with normal aorta (10 pg/ml; p = 8x10(-6), 95% CI: 70-159 pg/ml). Interestingly, our microarray data show that increased expression of inflammatory genes was associated with major clinical features within the MFS patients group; namely severity of the aortic root dilatation (HLA-DRB1 and HLA-DRB5 genes; r = 0.56 for both; False Discovery Rate(FDR) = 0%), ocular lens dislocation (RAET1L, CCL19 and HLA-DQB2; Fold Change (FC) = 1.8; 1.4; 1.5, FDR = 0%) and specific skeletal features (HLA-DRB1, HLA-DRB5, GZMK; FC = 8.8, 7.1, 1.3; FDR = 0%). Patients with progressive aortic disease had higher levels of Macrophage Colony Stimulating Factor (M-CSF) in blood. When comparing MFS aortic root vessel wall with non-MFS aortic root, increased numbers of CD4+ T-cells were found in the media (p = 0.02) and increased number of CD8+ T-cells (p = 0.003) in the adventitia of the MFS patients. CONCLUSION/SIGNIFICANCE: In conclusion, our results imply a modifying role of inflammation in MFS. Inflammation might be a novel therapeutic target in these patients
Location of studies and evidence of effects of herbivory on Arctic vegetation: a systematic map
Herbivores modify the structure and function of tundra ecosystems. Understanding their impacts is necessary to assess the responses of these ecosystems to ongoing environmental changes. However, the effects of herbivores on plants and ecosystem structure and function vary across the Arctic. Strong spatial variation in herbivore effects implies that the results of individual studies on herbivory depend on local conditions, i.e., their ecological context. An important first step in assessing whether generalizable conclusions can be produced is to identify the existing studies and assess how well they cover the underlying environmental conditions across the Arctic. This systematic map aims to identify the ecological contexts in which herbivore impacts on vegetation have been studied in the Arctic. Specifically, the primary question of the systematic map was: âWhat evidence exists on the effects of herbivores on Arctic vegetation?â
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