2,630 research outputs found
Isotropic, Nematic and Smectic A Phase Behaviour in a Fictitious Field
Phase behaviours of liquid crystals under external fields, conjugate to the
nematic order and smectic order, are studied within the framework of mean field
approximation developed by McMillan. It is found that phase diagrams, of
temperature vs interaction parameter of smectic A order, show several
topologically different types caused by the external fields. The influences of
the field conjugate to the smectic A phase, which is fictitious field, are
precisely discussed.Comment: To be published in J. Phys. Soc. Jpn. vol.73 No.
An epithelial cell destined for apoptosis signals its neighbors to extrude it by an actin- and myosin-dependent mechanism
AbstractBackground: Simple epithelia encase developing embryos and organs. Although these epithelia consist of only one or two layers of cells, they must provide tight barriers for the tissues that they envelop. Apoptosis occurring within these simple epithelia could compromise this barrier. How, then, does an epithelium remove apoptotic cells without disrupting its function as a barrier?Results: We show that apoptotic cells are extruded from a simple epithelium by the concerted contraction of their neighbors. A ring of actin and myosin forms both within the apoptotic cell and in the cells surrounding it, and contraction of the ring formed in the live neighbors is required for apoptotic cell extrusion, as injection of a Rho GTPase inhibitor into these cells completely blocks extrusion. Addition of apoptotic MDCK cells to an intact monolayer induces the formation of actin cables in the cells contacted, suggesting that the signal to form the cable comes from the dying cell. The signal is produced very early in the apoptotic process, before procaspase activation, cell shrinkage, or phosphatidylserine exposure. Remarkably, electrical resistance studies show that epithelial barrier function is maintained, even when large numbers of dying cells are being extruded.Conclusions: We propose that apoptotic cell extrusion is important for the preservation of epithelial barrier function during cell death. Our results suggest that an early signal from the dying cell activates Rho in live neighbors to extrude the apoptotic cell out of the epithelium
Applying machine learning to the problem of choosing a heuristic to select the variable ordering for cylindrical algebraic decomposition
Cylindrical algebraic decomposition(CAD) is a key tool in computational
algebraic geometry, particularly for quantifier elimination over real-closed
fields. When using CAD, there is often a choice for the ordering placed on the
variables. This can be important, with some problems infeasible with one
variable ordering but easy with another. Machine learning is the process of
fitting a computer model to a complex function based on properties learned from
measured data. In this paper we use machine learning (specifically a support
vector machine) to select between heuristics for choosing a variable ordering,
outperforming each of the separate heuristics.Comment: 16 page
Influence of Homeotropic Anchoring Walls upon Nematic and Smectic Phases
McMillan liquid crystal model sandwiched between strong homeotropic anchoring
walls is studied. Phase transitions between isotropic, nematic, and smectic A
phases are investigated for wide ranges of an interaction parameter and of the
system thickness. It is confirmed that the anchoring walls induce an increase
in transition temperatures, dissappearance of phase transitions, and an
appearance of non-spontaneous nematic phase. The similarity between influence
of anchoring walls and that of external fields is discussed.Comment: 5 pages, 6 figure
Polar Smectic Films
We report on a new experimental procedure for forming and studying polar
smectic liquid crystal films. A free standing smectic film is put in contact
with a liquid drop, so that the film has one liquid crystal/liquid interface
and one liquid crystal/air interface. This polar environment results in changes
in the textures observed in the film, including a boojum texture and a
previously unobserved spiral texture in which the winding direction of the
spiral reverses at a finite radius from its center. Some aspects of these
textures are explained by the presence of a Ksb term in the bulk elastic free
energy density that favors a combination of splay and bend deformations.Comment: 4 pages, REVTeX, 3 figures, submitted to PR
External-field-induced tricritical point in a fluctuation-driven nematic-smectic-A transition
We study theoretically the effect of an external field on the
nematic-smectic-A (NA) transition close to the tricritical point, where
fluctuation effects govern the qualitative behavior of the transition. An
external field suppresses nematic director fluctuations, by making them
massive. For a fluctuation-driven first-order transition, we show that an
external field can drive the transition second-order. In an appropriate liquid
crystal system, we predict the required magnetic field to be of order 10 T. The
equivalent electric field is of order .Comment: revtex, 4 pages, 1 figure; revised version, some equations have been
modifie
Ethical issues in the use of in-depth interviews: literature review and discussion
This paper reports a literature review on the topic of ethical issues in in-depth interviews. The review returned three
types of article: general discussion, issues in particular studies, and studies of interview-based research ethics. Whilst
many of the issues discussed in these articles are generic to research ethics, such as confidentiality, they often had particular
manifestations in this type of research. For example, privacy was a significant problem as interviews sometimes
probe unexpected areas. For similar reasons, it is difficult to give full information of the nature of a particular interview
at the outset, hence informed consent is problematic. Where a pair is interviewed (such as carer and cared-for) there are
major difficulties in maintaining confidentiality and protecting privacy. The potential for interviews to harm participants
emotionally is noted in some papers, although this is often set against potential therapeutic benefit. As well as
these generic issues, there are some ethical issues fairly specific to in-depth interviews. The problem of dual role is noted
in many papers. It can take many forms: an interviewer might be nurse and researcher, scientist and counsellor, or
reporter and evangelist. There are other specific issues such as taking sides in an interview, and protecting vulnerable
groups. Little specific study of the ethics of in-depth interviews has taken place. However, that which has shows some
important findings. For example, one study shows participants are not averse to discussing painful issues provided they
feel the study is worthwhile. Some papers make recommendations for researchers. One such is that they should consider
using a model of continuous (or process) consent rather than viewing consent as occurring once, at signature, prior
to the interview. However, there is a need for further study of this area, both philosophical and empirical
Infinite volume limit of the Abelian sandpile model in dimensions d >= 3
We study the Abelian sandpile model on Z^d. In dimensions at least 3 we prove
existence of the infinite volume addition operator, almost surely with respect
to the infinite volume limit mu of the uniform measures on recurrent
configurations. We prove the existence of a Markov process with stationary
measure mu, and study ergodic properties of this process. The main techniques
we use are a connection between the statistics of waves and uniform
two-component spanning trees and results on the uniform spanning tree measure
on Z^d.Comment: First version: LaTeX; 29 pages. Revised version: LaTeX; 29 pages. The
main result of the paper has been extended to all dimensions at least 3, with
a new and simplyfied proof of finiteness of the two-component spanning tree.
Second revision: LaTeX; 32 page
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