Are there new models of computation? Reply to Wegner and Eberbach

Wegner and Eberbach[Weg04b] have argued that there are fundamental limitations to Turing Machines as a foundation of computability and that these can be overcome by so-called superTuring models such as interaction machines, the [pi]calculus and the $-calculus. In this paper we contest Weger and Eberbach claims

Cell migration and capillary plexus formation in wounds and retinae

Cell migration is a fundamental biological phenomenon that is critical to the development and maintenance of tissues in multi-cellular organisms. This thesis presents a series of discrete mathematical models designed to study the migratory response of such cells when exposed to a variety of environmental stimuli. By applying these models to pertinent biological scenarios and benchmarking results against experimental data, novel insights are gained into the underlying cell behaviour. The process of angiogenesis is investigated first and models are developed for simulating capillary plexus expansion during both wound healing and retinal vascular development. The simulated cell migration is coupled to a detailed model of blood perfusion that allows prediction of dynamic flow-induced evolution of the nascent vascular architectures – the network topologies generated in each case are found to successfully reproduce a number of longitudinal experimental metrics. Moreover, in the case of retinal development, the resultant distributions of haematocrit and oxygen are found to be essential in generating vasculatures that resemble those observed in vivo. An alternative cell migration model is then derived that is capable of more accurately describing both individual and collective cell movement. The general model framework, which allows for biophysical cell-cell interactions and adaptive cell morphologies, is seen to have the potential for a range of applications. The value of the modelling approach is well demonstrated by benchmarking in silico cell movement against experimental data from an in vitro fibroblast scrape wound assay. The results subsequently reveal an unexplained discrepancy that provides an intriguing challenge for future studies

Challenging local realism with human choices

A Bell test is a randomized trial that compares experimental observations against the philosophical worldview of local realism. A Bell test requires spatially distributed entanglement, fast and high-efficiency detection and unpredictable measurement settings. Although technology can satisfy the first two of these requirements, the use of physical devices to choose settings in a Bell test involves making assumptions about the physics that one aims to test. Bell himself noted this weakness in using physical setting choices and argued that human `free will' could be used rigorously to ensure unpredictability in Bell tests. Here we report a set of local-realism tests using human choices, which avoids assumptions about predictability in physics. We recruited about 100,000 human participants to play an online video game that incentivizes fast, sustained input of unpredictable selections and illustrates Bell-test methodology. The participants generated 97,347,490 binary choices, which were directed via a scalable web platform to 12 laboratories on five continents, where 13 experiments tested local realism using photons, single atoms, atomic ensembles, and superconducting devices. Over a 12-hour period on 30 November 2016, participants worldwide provided a sustained data flow of over 1,000 bits per second to the experiments, which used different human-generated data to choose each measurement setting. The observed correlations strongly contradict local realism and other realistic positions in bipartite and tripartite scenarios. Project outcomes include closing the `freedom-of-choice loophole' (the possibility that the setting choices are influenced by `hidden variables' to correlate with the particle properties), the utilization of video-game methods for rapid collection of human generated randomness, and the use of networking techniques for global participation in experimental science.Comment: This version includes minor changes resulting from reviewer and editorial input. Abstract shortened to fit within arXiv limit

Calretinin positive neurons form an excitatory amplifier network in the spinal cord dorsal horn

Nociceptive information is relayed through the spinal cord dorsal horn, a critical area in sensory processing. The neuronal circuits in this region that underpin sensory perception must be clarified to better understand how dysfunction can lead to pathological pain. This study used an optogenetic approach to selectively activate spinal interneurons that express the calcium-binding protein calretinin (CR). We show that these interneurons form an interconnected network that can initiate and sustain enhanced excitatory signaling, and directly relay signals to lamina I projection neurons. Photoactivation of CR interneurons in vivo resulted in a significant nocifensive behavior that was morphine sensitive, caused a conditioned place aversion, and was enhanced by spared nerve injury. Furthermore, halorhodopsin-mediated inhibition of these interneurons elevated sensory thresholds. Our results suggest that dorsal horn circuits that involve excitatory CR neurons are important for the generation and amplification of pain and identify these interneurons as a future analgesic target

Open protocol design

Master'sMASTER OF ENGINEERIN