419 research outputs found
Nonequilibrium Fluctuations, Travelling Waves, and Instabilities in Active Membranes
The stability of a flexible fluid membrane containing a distribution of
mobile, active proteins (e.g. proton pumps) is shown to depend on the structure
and functional asymmetry of the proteins. A stable active membrane is in a
nonequilibrium steady state with height fluctuations whose statistical
properties are governed by the protein activity. Disturbances are predicted to
travel as waves at sufficiently long wavelength, with speed set by the normal
velocity of the pumps. The unstable case involves a spontaneous, pump-driven
undulation of the membrane, with clumping of the proteins in regions of high
activity.Comment: 4 two-column pages, two .eps figures included, revtex, uses eps
Computer simulations of hard pear-shaped particles
We report results obtained from Monte Carlo simulations investi-
gating mesophase formation in two model systems of hard pear-shaped
particles. The first model considered is a hard variant of the trun-
cated Stone-Expansion model previously shown to form nematic and
smectic mesophases when embedded within a 12-6 Gay-Berne-like po-
tential [1]. When stripped of its attractive interactions, however, this system is found to lose its liquid crystalline phases. For particles of length to breadth ratio k = 3, glassy behaviour is seen at high pressures, whereas for k = 5 several bi-layer-like domains are seen, with high intradomain order but little interdomain orientational correlation. For the second model, which uses a parametric shape parameter based on the generalised Gay-Berne formalism, results are presented for particles with elongation k = 3; 4 and 5. Here, the systems with k = 3 and 4 fail to display orientationally ordered phases, but that with k = 5 shows isotropic, nematic and, unusually for a hard-particle model, interdigitated smectic A2 phases.</p
Mechanochemical action of the dynamin protein
Dynamin is a ubiquitous GTPase that tubulates lipid bilayers and is
implicated in many membrane severing processes in eukaryotic cells. Setting the
grounds for a better understanding of this biological function, we develop a
generalized hydrodynamics description of the conformational change of large
dynamin-membrane tubes taking into account GTP consumption as a free energy
source. On observable time scales, dissipation is dominated by an effective
dynamin/membrane friction and the deformation field of the tube has a simple
diffusive behavior, which could be tested experimentally. A more involved,
semi-microscopic model yields complete predictions for the dynamics of the tube
and possibly accounts for contradictory experimental results concerning its
change of conformation as well as for plectonemic supercoiling.Comment: 17 pages, 4 figures; typos corrected, reference adde
Energy Transduction of Isothermal Ratchets: Generic Aspects and Specific Examples Close to and Far from Equilibrium
We study the energetics of isothermal ratchets which are driven by a chemical
reaction between two states and operate in contact with a single heat bath of
constant temperature. We discuss generic aspects of energy transduction such as
Onsager relations in the linear response regime as well as the efficiency and
dissipation close to and far from equilibrium. In the linear response regime
where the system operates reversibly the efficiency is in general nonzero.
Studying the properties for specific examples of energy landscapes and
transitions, we observe in the linear response regime that the efficiency can
have a maximum as a function of temperature. Far from equilibrium in the fully
irreversible regime, we find a maximum of the efficiency with values larger
than in the linear regime for an optimal choice of the chemical driving force.
We show that corresponding efficiencies can be of the order of 50%. A simple
analytic argument allows us to estimate the efficiency in this irreversible
regime for small external forces.Comment: 16 pages, 10 figure
Viscosities of the Gay-Berne nematic liquid crystal
We present molecular dynamics simulation measurements of the viscosities of
the Gay-Berne phenomenological model of liquid crystals in the nematic and
isotropic phases. The temperature dependence of the rotational and shear
viscosities, including the nonmonotonic behavior of one shear viscosity are in
good agreement with experimental data. The bulk viscosities are significantly
larger than the shear viscosities, again in agreement with experiment.Comment: 11 pages, 4 Postscript figures, Revte
Tissue factor in antiphospholipid antibody-induced pregnancy loss:a pro-inflammatory molecule
Fetal loss in patients with antiphospholipid antibodies (aPL) has been ascribed to thrombosis of placental vessels. However, we have shown that inflammation, specifically complement activation with generation of the anaphylotoxin C5a, is an essential mediator of fetal injury. We have analysed the role of tissue factor (TF) in a mouse model of aPL-induced pregnancy loss. TF is the major cellular activator of the coagulation cascade but also has cell signaling activity. Mice that received aPL-IgG showed strong TF staining throughout the decidua and on embryonic debris. This TF staining was not associated with either fibrin staining or thrombi in deciduas. The absence of fibrin deposition and thrombi suggests that TF-dependent activation of coagulation does not mediate aPL-induced pregnancy loss. We found that either blockade of TF with a monoclonal antibody in wild type mice or a genetic reduction of TF prevented aPL-induced inflammation and pregnancy loss indicated a pathogenic role for TF in aPL-induced pregnancy complications. In response to aPL-generated C5a, neutrophils express TF potentiating inflammation in the deciduas and leading to miscarriages. Importantly, we showed that TF in myeloid cells, but not fetal-derived cells (trophoblasts), was associated with fetal injury, suggesting that the site for pathologic TF expression is neutrophils. We found that TF expression in neutrophils contributes to respiratory burst and subsequent trophoblast injury and pregnancy loss induced by aPL. The identification of TF, acting as an important pro-inflammatory mediator in aPL-induced fetal injury, provides a new target for therapy to prevent pregnancy loss in the aPL syndrome
Community mobilisation to prevent violence against women and girls in eastern India through participatory learning and action with women's groups facilitated by accredited social health activists: a before-and-after pilot study
BACKGROUND: Almost one in three married Indian women have ever experienced physical, sexual, or emotional violence from husbands in their lifetime. We aimed to investigate the preliminary effects of community mobilisation through participatory learning and action groups facilitated by Accredited Social Health Activists (ASHAs), coupled with access to counselling, to prevent violence against women and girls in Jharkhand, eastern India. METHODS: We piloted a cycle of 16 participatory learning and action meetings with women's groups facilitated by ASHAs in rural Jharkhand. Participants identified common forms of violence against women and girls, prioritised the ones they wanted to address, developed locally feasible strategies to address them, implemented the strategies, and evaluated the process. We also trained two counsellors and two ASHA supervisors to support survivors, and gave ASHAs information about legal, health, and police services. We did a before-and-after pilot study involving baseline and endline surveys with group members to estimate preliminary effects of these activities on the acceptability of violence, prevalence of past year emotional and physical violence, and help-seeking. RESULTS: ASHAs successfully conducted monthly participatory learning and action meetings with 39 women's groups in 22 villages of West Singhbhum district, Jharkhand, between June 2016 and September 2017. We interviewed 59% (679/1149) of women registered with groups at baseline, and 63% (861/1371) at endline. More women reported that violence was unacceptable in all seven scenarios presented to them at endline compared to baseline (adjusted Odds Ratio [aOR]: 1.87, 95%: 1.39-2.52). Fewer women reported experiencing emotional violence from their husbands in the last 12 months (aOR: 0.55, 95% CI: 0.43-0.71), and more sought help if it occurred (aOR: 2.19, 95% CI: 1.51-3.17). In addition, fewer women reported experiencing emotional or physical violence from family members other than their husbands in the last 12 months (aOR: 0.41, 95% CI: 0.32-0.53, and aOR: 0.36, 95% CI: 0.26-0.50, respectively). CONCLUSION: Combining participatory learning and action meetings facilitated by ASHAs with access to counselling was an acceptable strategy to address violence against women and girls in rural communities of Jharkhand. The approach warrants further implementation and evaluation as part of a comprehensive response to violence
Polydispersity and ordered phases in solutions of rodlike macromolecules
We apply density functional theory to study the influence of polydispersity
on the stability of columnar, smectic and solid ordering in the solutions of
rodlike macromolecules. For sufficiently large length polydispersity (standard
deviation ) a direct first-order nematic-columnar transition is
found, while for smaller there is a continuous nematic-smectic and
first-order smectic-columnar transition. For increasing polydispersity the
columnar structure is stabilized with respect to solid perturbations. The
length distribution of macromolecules changes neither at the nematic-smectic
nor at the nematic-columnar transition, but it does change at the
smectic-columnar phase transition. We also study the phase behaviour of binary
mixtures, in which the nematic-smectic transition is again found to be
continuous. Demixing according to rod length in the smectic phase is always
preempted by transitions to solid or columnar ordering.Comment: 13 pages (TeX), 2 Postscript figures uuencode
Effect of a rigid nonpolar solute on the splay, bend elastic constants and on rotational viscosity coefficient of 4-4^\prime -n-octyl-cyanobiphenyl
The effect of a rigid nonpolar non-mesogenic solute, ``biphenyl'' which is
(C_{6}H_{5}-C_{6}H_{5}), on the splay and bend elastic constants and on the
rotational viscosity coefficient of (4,4^{\prime})-n-octyl-cyano biphenyl (8CB)
is reported. The experiments involve the measurement of voltage dependence of
capacitance of a cell filled with the mixture. Anomalous behavior of both
(K_{11}) and (\Delta \epsilon) near the (N-S_{A}) transition have been
observed.Comment: RevTeX - 8 figures. Accepted to be published in Physical Review
International Consensus Conference on Atopic Dermatitis II (ICCAD II * ): clinical update and current treatment strategies
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74915/1/j.1365-2133.148.s63.1.x.pd
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