497 research outputs found
A Geometric Tension Dynamics Model of Epithelial Convergent Extension
Epithelial tissue elongation by convergent extension is a key motif of animal
morphogenesis. On a coarse scale, cell motion resembles laminar fluid flow; yet
in contrast to a fluid, epithelial cells adhere to each other and maintain the
tissue layer under actively generated internal tension. To resolve this
apparent paradox, we formulate a model in which tissue flow occurs through
adiabatic remodelling of the cellular force balance causing local cell
rearrangement. We propose that the gradual shifting of the force balance is
caused by positive feedback on myosin-generated cytoskeletal tension. Shifting
force balance within a tension network causes active T1s oriented by the global
anisotropy of tension. Rigidity of cells against shape changes converts the
oriented internal rearrangements into net tissue deformation. Strikingly, we
find that the total amount of tissue extension depends on the initial magnitude
of anisotropy and on cellular packing order. T1s degrade this order so that
tissue flow is self-limiting. We explain these findings by showing that
coordination of T1s depends on coherence in local tension configurations,
quantified by a certain order parameter in tension space. Our model reproduces
the salient tissue- and cell-scale features of germ band elongation during
Drosophila gastrulation, in particular the slowdown of tissue flow after
approximately twofold extension concomitant with a loss of order in tension
configurations. This suggests local cell geometry contains morphogenetic
information and yields predictions testable in future experiments. Furthermore,
our focus on defining biologically controlled active tension dynamics on the
manifold of force-balanced states may provide a general approach to the
description of morphogenetic flow.Comment: 44 pages, 19 figure
A fabrication guide for planar silicon quantum dot heterostructures
We describe important considerations to create top-down fabricated planar
quantum dots in silicon, often not discussed in detail in literature. The
subtle interplay between intrinsic material properties, interfaces and
fabrication processes plays a crucial role in the formation of
electrostatically defined quantum dots. Processes such as oxidation, physical
vapor deposition and atomic-layer deposition must be tailored in order to
prevent unwanted side effects such as defects, disorder and dewetting. In two
directly related manuscripts written in parallel we use techniques described in
this work to create depletion-mode quantum dots in intrinsic silicon, and
low-disorder silicon quantum dots defined with palladium gates. While we
discuss three different planar gate structures, the general principles also
apply to 0D and 1D systems, such as self-assembled islands and nanowires.Comment: Accepted for publication in Nanotechnology. 31 pages, 12 figure
Fluctuation-Facilitated Charge Migration along DNA
We propose a model Hamiltonian for charge transfer along the DNA double helix
with temperature driven fluctuations in the base pair positions acting as the
rate limiting factor for charge transfer between neighboring base pairs. We
compare the predictions of the model with the recent work of J.K. Barton and
A.H. Zewail (Proc.Natl.Acad.Sci.USA, {\bf 96}, 6014 (1999)) on the unusual
two-stage charge transfer of DNA.Comment: 4 pages, 2 figure
Discourses of sexual relationships in a sample of German and British young people: a Q methodological study
Young people live in an environment which sexualises young people, particularly women, along traditional gender roles. This, in parallel with a silence about positive sexuality in policy development, means that sexual double standards prevail in young people’s lives. The aim of this study was to explore the discourses young women and men from two European countries, Germany and England, draw on when making sense of sexual relationships, and how these are steeped in the local cultural climate and messages. The study used Q methodology and included 65 German and English young people between 16 and 19 years of age. Six accounts emerged: sex as responsible, intimate and shared experience; sex as joint fun; ideal versus reality; sex has to be responsible, consensual and shared; caring relationships offer the perfect context for fulfilling sex; and equality between partners. The importance of cultural context in the availability of specific dominant and alternative discourses is discussed with a focus on how this influences young people’s sense-making with regard to sexuality and sexual relationships. Future directions for research are highlighted
Lessons about botulinum toxin A therapy from cervical dystonia patients drawing the course of disease: a pilot study
AIM OF THE STUDY: To compare the course of severity of cervical dystonia (CD) before and after long-term botulinum toxin (BoNT) therapy to detect indicators for a good or poor clinical outcome. PATIENTS AND METHODS: A total of 74 outpatients with idiopathic CD who were continuously treated with BoNT and who had received at least three injections were consecutively recruited. Patients had to draw the course of severity of CD from the onset of symptoms until the onset of BoNT therapy (CoDB graph), and from the onset of BoNT therapy until the day of recruitment (CoDA graph) when they received their last BoNT injection. Mean duration of treatment was 9.6 years. Three main types of CoDB and four main types of CoDA graphs could be distinguished. The demographic and treatment-related data of the patients were extracted from the patients' charts. RESULTS: The best outcome was observed in those patients who had experienced a clear, rapid response in the beginning. These patients had been treated with the lowest doses and with a low number of BoNT preparation switches. The worst outcome was observed in those 17 patients who had drawn a good initial improvement, followed by a secondary worsening. These secondary nonresponders had been treated with the highest initial and actual doses and with frequent BoNT preparation switches. A total of 12 patients were primary nonresponders and did not experience any improvement at all. No relation between the CoDB and CoDA graphs could be detected. Primary and secondary nonresponses were observed for all three CoDB types. The use of initial high doses as a relevant risk factor for the later development of a secondary nonresponse was confirmed. CONCLUSIONS: Patients' drawings of their course of disease severity helps to easily detect "difficult to treat" primary and secondary nonresponders to BoNT on the one hand, but also to detect "golden responders" on the other hand
Confirmation of Anomalous Dynamical Arrest in attractive colloids: a molecular dynamics study
Previous theoretical, along with early simulation and experimental, studies
have indicated that particles with a short-ranged attraction exhibit a range of
new dynamical arrest phenomena. These include very pronounced reentrance in the
dynamical arrest curve, a logarithmic singularity in the density correlation
functions, and the existence of `attractive' and `repulsive' glasses. Here we
carry out extensive molecular dynamics calculations on dense systems
interacting via a square-well potential. This is one of the simplest systems
with the required properties, and may be regarded as canonical for interpreting
the phase diagram, and now also the dynamical arrest. We confirm the
theoretical predictions for re-entrance, logarithmic singularity, and give the
first direct evidence of the coexistence, independent of theory, of the two
coexisting glasses. We now regard the previous predictions of these phenomena
as having been established.Comment: 15 pages,15 figures; submitted to Phys. Rev.
Significantly lower antigenicity of incobotulinumtoxin than abo- or onabotulinumtoxin
BACKGROUND: For many indications, BoNT/A is repetitively injected with the risk of developing neutralizing antibodies (NABs). Therefore, it is important to analyze whether there is a difference in antigenicity between the different licensed BoNT/A preparations. METHODS: In this cross-sectional study, the prevalence of NABs was tested by means of the sensitive mouse hemidiaphragm assay (MHDA) in 645 patients. Patients were split into those having exclusively been treated with the complex protein-free incoBoNT/A preparation (CF-MON group) and those having started BoNT/A therapy with a complex protein-containing BoNT/A preparation (CC-I group). This CC-I group was split into those patients who remained either on abo- or onaBoNT/A (CC-MON group) and those who had been treated with at least two BoNT/A preparations (CC-SWI group). To balance treatment duration, only CC-MON patients who did not start their BoNT/A therapy more than 10 years before recruitment (CC-MON-10 group) were further analyzed. The log-rank test was used to compare the prevalence of NABs in the CF-MON and CC-MON-10 group. RESULTS: In the CF-MON subgroup, no patient developed NABs. In the CC-I group, 84 patients were NAB-positive. NABs were found in 33.3% of those who switched preparations (CC-SWI) and in 5.9% of the CC-MON-10 group. Kaplan-Meier curves for remaining NAB-negative under continuous BoNT/A therapy were significantly different (p < 0.035) between the CF-MON and CC-MON-10 group. CONCLUSION: Frequent injections of a complex protein-containing BoNT/A preparation are associated with significantly higher risks of developing NABs than injections with the same frequency using the complex protein-free incoBoNT/A preparation
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