1,972 research outputs found
All-Optical Nanopositioning of High-Q Silica Microspheres
A tunable, all-optical, coupling method has been realized for a
high-\textit{Q} silica microsphere and an optical waveguide. By means of a
novel optical nanopositioning method, induced thermal expansion of an
asymmetric microsphere stem for laser powers up to 171~mW has been observed and
used to fine tune the microsphere-waveguide coupling. Microcavity displacements
ranging from (0.612~~0.13) -- (1.5 0.13) m and nanometer scale
sensitivities varying from (2.81 0.08) -- (7.39 0.17) nm/mW, with
an apparent linear dependency of coupling distance on stem laser heating, were
obtained. Using this method, the coupling was altered such that different
coupling regimes could be explored for particular samples. This tunable
coupling method, in principle, could be incorporated into lab-on-a-chip
microresonator systems, photonic molecule systems, and other nanopositioning
frameworks.Comment: 6pages,4figure
The Evolution of Active Droplets in Chemorobotic Platforms
There is great interest in oil-in-water droplets as simple systems that display astonishingly complex behaviours. Recently, we reported a chemorobotic platform capable of autonomously exploring and evolving the behaviours these droplets can exhibit. The platform enabled us to undertake a large number of reproducible experiments, allowing us to probe the non-linear relationship between droplet composition and behaviour. Herein we introduce this work, and also report on the recent developments we have made to this system. These include new platforms to simultaneously evolve the dropletsâ physical and chemical environments and the inclusion of selfreplicating molecules in the droplets
Evolutionary Models for Formation of Network Motifs and Modularity in the Saccharomyces Transcription Factor Network
Many natural and artificial networks contain overrepresented subgraphs, which have been termed network motifs. In this article, we investigate the processes that led to the formation of the two most common network motifs in eukaryote transcription factor networks: the bi-fan motif and the feed-forward loop. Around 100 million y ago, the common ancestor of the Saccharomyces clade underwent a whole-genome duplication event. The simultaneous duplication of the genes created by this event enabled the origin of many network motifs to be established. The data suggest that there are two primary mechanisms that are involved in motif formation. The first mechanism, enabled by the substantial plasticity in promoter regions, is rewiring of connections as a result of positive environmental selection. The second is duplication of transcription factors, which is also shown to be involved in the formation of intermediate-scale network modularity. These two evolutionary processes are complementary, with the pre-existence of network motifs enabling duplicated transcription factors to bind different targets despite structural constraints on their DNA-binding specificities. This process may facilitate the creation of novel expression states and the increases in regulatory complexity associated with higher eukaryotes
Mechanical design principles of a mitotic spindle.
An organised spindle is crucial to the fidelity of chromosome segregation, but the relationship between spindle structure and function is not well understood in any cell type. The anaphase B spindle in fission yeast has a slender morphology and must elongate against compressive forces. This 'pushing' mode of chromosome transport renders the spindle susceptible to breakage, as observed in cells with a variety of defects. Here we perform electron tomographic analyses of the spindle, which suggest that it organises a limited supply of structural components to increase its compressive strength. Structural integrity is maintained throughout the spindle's fourfold elongation by organising microtubules into a rigid transverse array, preserving correct microtubule number and dynamically rescaling microtubule length
Hydantoin-bridged medium ring scaffolds by migratory insertion of urea-tethered nitrile anions into aromatic C-N bonds
Bicyclic or tricyclic nitrogen-containing heterocyclic scaffolds were constructed rapidly by intramolecular nucleophilic aromatic substitution of metallated nitriles tethered by a urea linkage to a series of electronically unactivated heterocyclic precursors. The substitution reaction constitutes a ring expansion, enabled by the conformationally constrained tether between the nitrile and the heterocycle. Attack of the metallated urea leaving group on the nitrile generates a hydantoin that bridges the polycyclic products. X-ray crystallography reveals ring-dependant strain within the hydantoin
Rethinking rewilding: A response to JĂžrgensen
In this article we respond to and challenge JĂžrgensenâs criticisms of the concept of rewilding in her paper âRethinking rewildingâ, published this year in Geoforum. JĂžrgensen argues that ârewildingâ has become a âplastic wordâ, one that has been stretched to the point where it lacks definitional precision, at risk of becoming âthe go-to blanket solution to environmental problemsâ. She also argues that the practice of rewilding is premised upon the dissociation of humans from the rest of nature and reproduces anti-human NatureâCulture binaries, rightly lambasted by critics of wilderness narratives in conservation practice. In response to these criticisms we challenge JĂžrgensen on two points. Firstly we argue that the problems of âplasticityâ and definitional imprecision can be rectified by highlighting and foregrounding the quality that we believe is at the core of all rewilding definitions and efforts: non-human autonomy. Secondly, we challenge JĂžrgensenâs broad claim that sees the collapse of ârewildingâ into anti-human wilderness management. We do so by reflecting on two points; the dynamic humanânon-human entanglements embedded within rewilding practice(s) and by arguing for rewilding as a âwild experimentâ. We make these points through the examination of two actually existing examples of rewilding
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Is communication guidance mistaken? Qualitative study of parent-oncologist communication in childhood cancer
background: Guidance encourages oncologists to engage patients and relatives in discussing the emotions that accompany cancer diagnosis and treatment. We investigated the perspectives of parents of children with leukaemia on the role of paediatric oncologists in such discussion.
methods: Qualitative study comprising 33 audio-recorded parentâoncologist consultations and semi-structured interviews with 67 parents during the year following diagnosis.
results: Consultations soon after the diagnosis were largely devoid of overt discussion of parental emotion. Interviewed parents did not describe a need for such discussion. They spoke of being comforted by oncologistsâ clinical focus, by the biomedical information they provided and by their calmness and constancy. When we explicitly asked parents 1 year later about the oncologistsâ role in emotional support, they overwhelmingly told us that they did not want to discuss their feelings with oncologists. They wanted to preserve the oncologistsâ focus on their childâs clinical care, deprecated anything that diverted from this and spoke of the value of boundaries in the parentâoncologist relationship.
conclusion: Parents were usually comforted by oncologists, but this was not achieved in the way suggested by communication guidance. Communication guidance would benefit from an enhanced understanding of how emotional support is experienced by those who rely on it
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