1,118 research outputs found
A Bayesian test for the appropriateness of a model in the biomagnetic inverse problem
This paper extends the work of Clarke [1] on the Bayesian foundations of the
biomagnetic inverse problem. It derives expressions for the expectation and
variance of the a posteriori source current probability distribution given a
prior source current probability distribution, a source space weight function
and a data set. The calculation of the variance enables the construction of a
Bayesian test for the appropriateness of any source model that is chosen as the
a priori infomation. The test is illustrated using both simulated
(multi-dipole) data and the results of a study of early latency processing of
images of human faces.
[1] C.J.S. Clarke. Error estimates in the biomagnetic inverse problem.
Inverse Problems, 10:77--86, 1994.Comment: 13 pages, 16 figures. Submitted to Inverse Problem
Imprinted Networks as Chiral Pumps
We investigate the interaction between a chirally imprinted network and a
solvent of chiral molecules. We find, a liquid crystalline polymer network is
preferentially swollen by one component of a racemic solvent. This ability to
separate is linked to the chiral order parameter of the network, and can be
reversibly controlled via temperature or a mechanical deformation. It is
maximal near the point at which the network loses its imprinted structure. One
possible practical application of this effect would be a mechanical device for
sorting mixed chiral molecules.Comment: 4 pages, 5 figure
Untwisting of a Strained Cholesteric Elastomer by Disclination Loop Nucleation
The application of a sufficiently strong strain perpendicular to the pitch
axis of a monodomain cholesteric elastomer unwinds the cholesteric helix.
Previous theoretical analyses of this transition ignored the effects of Frank
elasticity which we include here. We find that the strain needed to unwind the
helix is reduced because of the Frank penalty and the cholesteric state becomes
metastable above the transition. We consider in detail a previously proposed
mechanism by which the topologically stable helical texture is removed in the
metastable state, namely by the nucleation of twist disclination loops in the
plane perpendicular to the pitch axis. We present an approximate calculation of
the barrier energy for this nucleation process which neglects possible spatial
variation of the strain fields in the elastomer, as well as a more accurate
calculation based on a finite element modeling of the elastomer.Comment: 12 pages, 9 figure
Chirality transfer and stereo-selectivity of imprinted cholesteric networks
Imprinting of cholesteric textures in a polymer network is a method of
preserving a macroscopically chiral phase in a system with no molecular
chirality. By modifying the elastics properties of the network, the resulting
stored helical twist can be manipulated within a wide range since the
imprinting efficiency depends on the balance between the elastics constants and
twisting power at network formation. One spectacular property of phase
chirality imprinting is the created ability of the network to adsorb
preferentially one stereo-component from a racemic mixture. In this paper we
explore this property of chirality transfer from a macroscopic to the molecular
scale. In particular, we focus on the competition between the phase chirality
and the local nematic order. We demonstrate that it is possible to control the
subsequent release of chiral solvent component from the imprinting network and
the reversibility of the stereo-selective swelling by racemic solvents
Stereo-selective swelling of imprinted cholesteric networks
Molecular chirality, and the chiral symmetry breaking of resulting
macroscopic phases, can be topologically imprinted and manipulated by
crosslinking and swelling of polymer networks. We present a new experimental
approach to stereo-specific separation of chiral isomers by using a cholesteric
elastomer in which a helical director distribution has been topological
imprinted by crosslinking. This makes the material unusual in that is has a
strong phase chirality, but no molecular chirality at all; we study the nature
and parameters controlling the twist-untwist transition. Adding a racemic
mixture to the imprinted network results in selective swelling by only the
component of ``correct'' handedness. We investigate the capacity of demixing in
a racemic environment, which depends on network parameters and the underlying
nematic order
Untwisting of a cholesteric elastomer by a mechanical field
A mechanical strain field applied to a monodomain cholesteric elastomer will
unwind the helical director distribution. There is an analogy with the
classical problem of an electric field applied to a cholesteric liquid crystal,
but with important differences. Frank elasticity is of minor importance unless
the gel is very weak. The interplay is between director anchoring to the rubber
elastic matrix and the external mechanical field. Stretching perpendicular to
the helix axis induces the uniform unwound state via the elimination of sharp,
pinned twist walls above a critical strain. Unwinding through conical director
states occurs when the elastomer is stretched along the helical axis.Comment: 4 pages, RevTeX 3 style, 3 EPS figure
Recommended from our members
Circulating Biomarkers to Identify Responders in Cardiac Cell therapy.
Bone marrow mononuclear cell (BM-MNC) therapy in ST-elevation acute myocardial infarction (STEMI) has no biological inclusion criteria. Here, we analyzed 63 biomarkers and cytokines in baseline plasma samples from 77 STEMI patients treated with BM-MNCs in the TIME and Late-TIME trials as well as 61 STEMI patients treated with placebo. Response to cell therapy was defined by changes in left ventricular ejection fraction, systolic/diastolic volumes, and wall motion indexes. We investigated the clinical value of circulating proteins in outcome prediction using significance testing, partial least squares discriminant analysis, and receiver operating characteristic (ROC) analysis. Responders had higher biomarker levels (76-94% elevated) than non-responders. Several biomarkers had values that differed significantly (P < 0.05) between responders and non-responders including stem cell factor, platelet-derived growth factor, and interleukin-15. We then used these lead candidates for ROC analysis and found multiple biomarkers with values areas under the curve >0.70 including interleukin 15. These biomarkers were not involved in the placebo-treated subjects suggesting that they may have predictive power. We conclude that plasma profiling after STEMI may help identify patients with a greater likelihood of response to cell-based treatment. Prospective trials are needed to assess the predictive value of the circulating biomarkers
Stress and prevalence of hearing problems in the Swedish working population
<p>Abstract</p> <p>Background</p> <p>Current human and experimental studies are indicating an association between stress and hearing problems; however potential risk factors have not been established. Hearing problems are projected to become among the top ten disabilities according to the WHO in the near future. Therefore a better understanding of the relationships between stress and hearing is warranted. Here we describe the prevalence of two common hearing problems, i.e. hearing complaints and tinnitus, in relation to different work-and health-related stressors.</p> <p>Methods</p> <p>A total of 18,734 individuals were invited to participate in the study, out of which 9,756 (52%) enrolled.</p> <p>Results</p> <p>The results demonstrate a clear and mostly linear relationship between higher prevalence of hearing problems (tinnitus or hearing loss or both) and different stressors, e.g. occupational, poorer self-rated health, long-term illness, poorer sleep quality, and higher burnout scores.</p> <p>Conclusions</p> <p>The present study unambiguously demonstrates associations between hearing problems and various stressors that have not been previously described for the auditory system. These findings will open new avenues for future investigations.</p
Separate processing of texture and form in the ventral stream : evidence from fMRI and visual agnosia.
Real-life visual object recognition requires the processing of more than just geometric (shape, size, and orientation) properties. Surface properties such as color and texture are equally important, particularly for providing information about the material properties of objects. Recent neuroimaging research suggests that geometric and surface properties are dealt with separately, within the lateral occipital cortex (LOC) and the collateral sulcus (CoS), respectively. Here we compared objects that either differed in aspect ratio or in surface texture only, keeping all other visual properties constant. Results on brain-intact participants confirmed that surface texture activates an area in the posterior CoS, quite distinct from the area activated by shape within LOC. We also tested two patients with visual object agnosia, one of whom (DF) performed well on the texture task but at chance on the shape task, while the other (MS) showed the converse pattern. This behavioral double dissociation was matched by a parallel neuroimaging dissociation, with activation in CoS but not LOC in patient DF, and activation in LOC but not CoS in patient MS. These data provide presumptive evidence that the areas respectively activated by shape and texture play a causally necessary role in the perceptual discrimination of these features
Achieving Consensus in the Development of an Online Intervention Designed to Effectively Support Midwives in Work-Related Psychological Distress: Protocol for a Delphi Study
BACKGROUND: The development of an online intervention designed to effectively support midwives in work-related psychological distress will be challenging due to the ethical, practical, and therapeutic issues surrounding its design. Related literature suggests that midwives may require an anonymous, confidential, and therapeutic platform that facilitates amnesty and nonpunitive approaches to remedy ill health. However, it is unclear which requirements may be most salient to midwifery populations. OBJECTIVE: The objective of this paper is to describe the design of a Delphi study, intended to achieve expert consensus on the needs of midwives in work-related psychological distress who may be supported via an online intervention. This protocol may also serve as a research framework for similar studies to be modeled upon. METHODS: A heterogeneous sample of at least thirty experts on psychological well-being and distress associated with midwifery work will be recruited. Their opinions regarding the development of an online intervention designed to support midwives in work-related psychological distress will be collected through 2 rounds of questioning, via the Delphi Technique. When 60% (≥18, assuming the minimum is 30) of panelists score within 2 adjacent points on a 7-point scale, consensus will be acknowledged. This Delphi study protocol will invite both qualitative and quantitative outcomes. RESULTS: This study is currently in development. It is financially supported by a full-time scholarship at the Centre for Technology Enabled Health Research at Coventry University (Coventry, UK). The implementation of this Delphi study is anticipated to occur during the autumn of 2015. CONCLUSIONS: The results of this study will direct the development of an online intervention designed to support midwives in work-related psychological distress, summarize expert driven consensus, and direct future research
- …