87 research outputs found
Mechanics of Reversible Unzipping
We study the mechanics of a reversible decohesion (unzipping) of an elastic
layer subjected to quasi-static end-point loading. At the micro level the
system is simulated by an elastic chain of particles interacting with a rigid
foundation through breakable springs. Such system can be viewed as prototypical
for the description of a wide range of phenomena from peeling of polymeric
tapes, to rolling of cells, working of gecko's fibrillar structures and
denaturation of DNA. We construct a rigorous continuum limit of the discrete
model which captures both stable and metastable configurations and present a
detailed parametric study of the interplay between elastic and cohesive
interactions. We show that the model reproduces the experimentally observed
abrupt transition from an incremental evolution of the adhesion front to a
sudden complete decohesion of a macroscopic segment of the adhesion layer. As
the microscopic parameters vary the macroscopic response changes from
quasi-ductile to quasi-brittle, with corresponding decrease in the size of the
adhesion hysteresis. At the micro-scale this corresponds to a transition from a
`localized' to a `diffuse' structure of the decohesion front (domain wall). We
obtain an explicit expression for the critical debonding threshold in the limit
when the internal length scales are much smaller than the size of the system.
The achieved parametric control of the microscopic mechanism can be used in the
design of new biological inspired adhesion devices and machines
Efferent Projections of Prokineticin 2 Expressing Neurons in the Mouse Suprachiasmatic Nucleus
The suprachiasmatic nucleus (SCN) in the hypothalamus is the predominant circadian clock in mammals. To function as a pacemaker, the intrinsic timing signal from the SCN must be transmitted to different brain regions. Prokineticin 2 (PK2) is one of the candidate output molecules from the SCN. In this study, we investigated the efferent projections of PK2-expressing neurons in the SCN through a transgenic reporter approach. Using a bacterial artificial chromosome (BAC) transgenic mouse line, in which the enhanced green fluorescence protein (EGFP) reporter gene expression was driven by the PK2 promoter, we were able to obtain an efferent projections map from the EGFP-expressing neurons in the SCN. Our data revealed that EGFP-expressing neurons in the SCN, hence representing some of the PK2-expressing neurons, projected to many known SCN target areas, including the ventral lateral septum, medial preoptic area, subparaventricular zone, paraventricular nucleus, dorsomedial hypothalamic nucleus, lateral hypothalamic area and paraventricular thalamic nucleus. The efferent projections of PK2-expressing neurons supported the role of PK2 as an output molecule of the SCN
Using C. elegans to discover therapeutic compounds for ageing-associated neurodegenerative diseases
Age-associated neurodegenerative disorders such as Alzheimer’s disease are a major public health challenge, due to the demographic increase in the proportion of older individuals in society. However, the relatively few currently approved drugs for these conditions provide only symptomatic relief. A major goal of neurodegeneration research is therefore to identify potential new therapeutic compounds that can slow or even reverse disease progression, either by impacting directly on the neurodegenerative process or by activating endogenous physiological neuroprotective mechanisms that decline with ageing. This requires model systems that can recapitulate key features of human neurodegenerative diseases that are also amenable to compound screening approaches. Mammalian models are very powerful, but are prohibitively expensive for high-throughput drug screens. Given the highly conserved neurological pathways between mammals and invertebrates, Caenorhabditis elegans has emerged as a powerful tool for neuroprotective compound screening. Here we describe how C. elegans has been used to model various human ageing-associated neurodegenerative diseases and provide an extensive list of compounds that have therapeutic activity in these worm models and so may have translational potential
Jasmonic acid elicits oxidative defense and detoxification systems in Cucumis melo L. cells
Recent advances in gecko adhesion and friction mechanisms and development of gecko-inspired dry adhesive surfaces
An expression for contact area between particles in a powder compact in terms of the porosity
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