244 research outputs found
Instability and front propagation in laser-tweezed lipid bilayer tubules
We study the mechanism of the `pearling' instability seen recently in
experiments on lipid tubules under a local applied laser intensity. We argue
that the correct boundary conditions are fixed chemical potentials, or surface
tensions \Sigma, at the laser spot and the reservoir in contact with the
tubule. We support this with a microscopic picture which includes the intensity
profile of the laser beam, and show how this leads to a steady-state flow of
lipid along the surface and gradients in the local lipid concentration and
surface tension (or chemical potential). This leads to a natural explanation
for front propagation and makes several predictions based on the tubule length.
While most of the qualitative conclusions of previous studies remain the same,
the `ramped' control parameter (surface tension) implies several new
qualitative results. We also explore some of the consequences of front
propagation into a noisy (due to pre-existing thermal fluctuations) unstable
medium.Comment: 12 page latex + figures using epsf.sty to be published in Journal de
Physique II, January 199
Budding and Domain Shape Transformations in Mixed Lipid Films and Bilayer Membranes
We study the stability and shapes of domains with spontaneous curvature in
fluid films and membranes, embedded in a surrounding membrane with zero
spontaneous curvature. These domains can result from the inclusion of an
impurity in a fluid membrane, or from phase separation within the membrane. We
show that for small but finite line and surface tensions and for finite
spontaneous curvatures, an equilibrium phase of protruding circular domains is
obtained at low impurity concentrations. At higher concentrations, we predict a
transition from circular domains, or "caplets", to stripes. In both cases, we
calculate the shapes of these domains within the Monge representation for the
membrane shape. With increasing line tension, we show numerically that there is
a budding transformation from stable protruding circular domains to spherical
buds. We calculate the full phase diagram, and demonstrate a two triple points,
of respectively bud-flat-caplet and flat-stripe-caplet coexistence.Comment: 14 pages, to appear in Phys Rev
Tectonic-sedimentary evolution of the northern margin of Gondwana during Late Palaeozoic – Early Cenozoic time in the Eastern Mediterranean region: evidence from the Central Taurus Mountains, Turkey.
The Taurus Mountains are an E-W trending mountain range in southern Turkey, with an
elevation of up to 3500 m. In the south central Taurides, the Beysehir-Hoyran-Hadim
nappes, a series of thrust sheets of Palaeozoic to Early Cenozoic age, are emplaced onto
a relatively autochthonous Tauride platform, known as the Geyik Dag. These thrust
sheets consist of a variety of discrete tectonostratigraphic units of continental platform,
rifted margin and oceanic (ophiolitic) origin. It is generally accepted that the relatively
autochthonous Tauride platform and the associated thrust sheets restore as a north-facing
passive margin during Jurassic–Cretaceous time; however, the Triassic and earlier
tectonic setting of the Tauride units is contentious. New data (mainly structural and
sedimentological) presented here tests contrasting tectonic models of Late Palaeozoic –
Early Mesozoic Tethys ocean evolution. Also, new light is shed on the Late Cretaceous
and Early Cenozoic break-up and emplacement of the Tauride units during closure of
Tethys.
The Late Palaeozoic Tauride stratigraphy consists of shallow-marine carbonate,
sandstone and mudstone, characteristic of a proximal passive margin. Detailed
stratigraphic logging, facies interpretation, compositional analysis and geochemical
evidence supports a passive margin setting, with sediment derived from the Tauride
“basement”. Early – Middle Triassic mixed siliciclastic/carbonate sediments are
interpreted as representing rifting and subsidence. Late Triassic coarser terrestrial
clastics (Cayir Formation) are considered to represent a pulse of rift-related flexural
uplift. Sediment provenance during this time was from the underlying Tauride platform
to the north of the studied area. A previous hypothesis that a Palaeotethyan ocean closed
in this area during latest Triassic “Cimmerian” orogenesis is discounted. Instead,
structural and sedimentary data suggest that all of the deformation relates to Late
Cretaceous – Early Cenozoic southward emplacement of the Beysehir-Hoyran-Hadim
nappes. A first phase of thrusting (thin-skinned) emplaced ophiolite and distal margin
units, whilst a second phase (thick-skinned) thrust platform lithologies southwards onto
the foreland. Evidence is also summarised, notably from the Palaeozoic – Early
Mesozoic Konya Complex to the north, which illustrates the relation of the Tauride
platform to other geological terranes in Turkey and elsewhere in the Alpine-Himalayan
orogenic belt. This thesis increases understanding of large-scale tectonic and
sedimentary processes associated with continental margins and orogenic development
Enhanced effects of combined cognitive bias modification and computerised cognitive behaviour therapy on social anxiety
This study examines whether combined cognitive bias modification for interpretative biases (CBM-I) and computerised cognitive behaviour therapy (C-CBT) can produce enhanced positive effects on interpretation biases and social anxiety. Forty socially anxious students were randomly assigned into two conditions, an intervention group (positive CBM-I + C-CBT) or an active control (neutral CBM-I + C-CBT). At pre-test, participants completed measures of social anxiety, interpretative bias, cognitive distortions, and social and work adjustment. They were exposed to 6 × 30 min sessions of web-based interventions including three sessions of either positive or neutral CBM-I and three sessions of C-CBT, one session per day. At post-test and two-week follow-up, participants completed the baseline measures. A combined positive CBM-I + C-CBT produced less negative interpretations of ambiguous situations than neutral CBM-I + C-CBT. The results also showed that both positive CBM-I + C-CBT and neutral CBM-I + C-CBT reduced social anxiety and cognitive distortions as well as improving work and social adjustment. However, greater effect sizes were observed in the positive CBM-I + C-CBT condition than the control. This indicates that adding positive CBM-I to C-CBT enhanced the training effects on social anxiety, cognitive distortions, and social and work adjustment compared to the neutral CBM-I + C-CBT condition
Understanding the enablers and barriers to implementing a patient-led escalation system: a qualitative study
Background: The management of acute deterioration following surgery remains highly variable. Patients and families can play an important role in identifying early signs of deterioration but effective contribution to escalation of care can be practically difficult to achieve. This paper reports the enablers and barriers to the implementation of patient-led escalation systems found during a process evaluation of a quality improvement programme Rescue for Emergency Surgery Patients Observed to uNdergo acute Deterioration (RESPOND). Methods: The research used ethnographic methods, including over 100 hours of observations on surgical units in three English hospitals in order to understand the everyday context of care. Observations focused on the coordination of activities such as handovers and how rescue featured as part of this. We also conducted 27 interviews with a range of clinical and managerial staff and patients. We employed a thematic analysis approach, combined with a theoretically focused implementation coding framework, based on Normalisation Process Theory. Results: We found that organisational infrastructural support in the form of a leadership support and clinical care outreach teams with capacity were enablers in implementing the patient-led escalation system. Barriers to implementation included making changes to professional practice without discussing the value and legitimacy of operationalising patient concerns, and ensuring equity of use. We found that organisational work is needed to overcome patient fears about disrupting social and cultural norms. Conclusions: This paper reveals the need for infrastructural support to facilitate the implementation of a patient-led escalation system, and leadership support to normalise the everyday process of involving patients and families in escalation. This type of system may not achieve its goals without properly understanding and addressing the concerns of both nurses and patients
In vitro biomarker discovery in the parasitic flatworm Fasciola hepatica for monitoring chemotherapeutic treatment
The parasitic flatworm Fasciola hepatica is a global food security risk. With no vaccines, the sustainability of triclabendazole (TCBZ) is threatened by emerging resistance. F. hepatica excretory/secretory (ES) products can be detected in host faeces and used to estimate TCBZ success and failure. However, there are no faecal based molecular diagnostics dedicated to assessing drug failure or resistance to TCBZ in the field. Utilising in vitro maintenance and sub-proteomic approaches two TCBZ stress ES protein response fingerprints were identified: markers of non-killing and lethal doses. This study provides candidate protein/peptide biomarkers to validate for detection of TCBZ failure and resistance
Instabilities and Oscillations in Isotropic Active Gels
We present a generic formulation of the continuum elasticity of an isotropic
crosslinked active gel. The gel is described by a two-component model
consisting of an elastic network coupled frictionally to a permeating fluid.
Activity is induced by active crosslinkers that undergo an ATP-activated cycle
and transmit forces to the network. The on/off dynamics of the active
crosslinkers is described via rate equations for unbound and bound motors. For
large activity motors yield a contractile instability of the network. At
smaller values of activity, the on/off motor dynamics provides an effective
inertial drag on the network that opposes elastic restoring forces, resulting
in spontaneous oscillations. Our work provides a continuum formulation that
unifies earlier microscopic models of oscillations in muscle sarcomeres and a
generic framework for the description of the large scale properties of
isotropic active solids.Comment: 13 pages, 5 figure
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