What impact have local electric field fluctuations on neuronal activity? Recording extracellular action potential is one of the primary methods to study brain function in the living animal. Understanding and quantifying the effect of the local field potential on the transmembrane potential of neurones is crucial for determining whether and when a given synaptic input will cause neurones to initiate an action potential. Since the days of Hodgkin-Huxley and their equations, neuronal membrane and extended dendritic as well as axonal structures have been modelled using one-dimensional cable theory in combination with linear or nonlinear time, voltage- and ligand-gated membrane conductances. In this entire body of work a common assumption was that the extracellular potential (Ve) is uniform, i.e. it does not depend on space, and is constant in time. Both assumptions, however, are known to be wrong - otherwise one could not record action potentials from outside neurones - but were justified by arguing that contributions of a non-uniform Ve(x, t) could be neglected. We propose to study theoretically the effect of a non-uniform and dynamic Ve on different levels of neuronal complexity: (a) on a single, unbranched cable model of a neurone, (b) on hippocampal pyramidal neurones with realistic dendritic morphology and electrophysiological signature and (c) on a population of simplified cortical cells exhibiting typical morphology and activity. In the first two stages, existing simulators from Prof. Christof Koch's lab (California Institute of Technology, USA) will be implemented as well as experimentally measured spatial and temporal Ve distributions from electrode arrays from Prof. Gyorgy Buzsaki's lab (Rutgers, USA). Recent in vitro studies indicate that in hippocampus electric field effects play a crucial role on neuronal synchronization. Based on these results, in the third stage, a reduced model will help us study the same effects on a neuronal population where features of small-world dynamics and synchronization will be investigated. All our theoretical conclusions will be compared to detailed experimental measurements.What effects do large excursions of Ve (up to 10 mV/mm for hippocampal sharp waves) have on the spiking activity of individual hippocampal pyramidal neurones? Will the firing of the neurone become entrained to the electric field through direct, so-called ephaptic, effects? How are these phenomena reflected upon a population of neurones firing? Are these effects manifested differently on the typical oscillatory frequencies that are attributed to diverse behavioural states? These are just a few of the questions we seek to investigate with this proposal.

Earthquakes, produced by rapid slip on faults, account for the majority of deaths from a range of natural disasters which amounts to about 60,000 people a year worldwide - around 90 percent of which occur in developing countries. Slip can occur in three ways on faults. These are (1) earthquake slip; (2) stable fault creep driven by plate tectonic loading rates; and (3) episodic slow slip events, where fault slip spontaneously accelerates but never reaches earthquake slip speeds. Episodic slow slip events can release the same amount of energy as earthquakes but over days to weeks rather than seconds to minutes. They most commonly occur in certain regions of subduction zones and have been linked to elevated pore pressures. These three modes of fault slip are vital to understand, as episodic slow slip and fault creep relieve stress build up and reduce seismic hazard, yet also transfer stress from one part of the fault to another, ultimately affecting the nucleation of destructive earthquakes. In this project, we will provide physical constraints from combined experiments and numerical modelling to determine the controlling factors leading to stable fault creep, episodic slow slip, or earthquakes. As yet, it is not understood what puts the brakes on some instabilities creating slow fault slip yet allows others to accelerate to rapid slip speeds that cause earthquakes. A transition of some sort from unstable frictional sliding (typically viewed as leading to earthquakes) to stable frictional sliding (typically viewed as leading to fault creep) while the sliding velocity is increasing must promote sustained slow slip on faults. The nature of this stability transition is widely debated and the range of conditions under which it may occur are ill defined. We will investigate the key hypotheses proposed to explain such stability transition and the resulting slow slip events, which include (1) evolution in friction properties related to very slow slip rates at elevated temperatures, (2) the role of pore fluid pressure on stability transitions, where small increases in pore volume of the granular shearing material in the fault produces a large decrease in pore pressure resulting in increase in the shear resistance (dilatant strengthening), and (3) spatial variation in fault properties and conditions leading to a situation where nucleation of an earthquake can occur but is limited by adjacent regions with stable frictional properties. The work will involve integrated laboratory experiments and numerical modelling. Controlled lab experiments will measure the evolution of fault friction under previously unexplored temperature, pore fluid pressure, and slip rate conditions relevant to natural faults. We will quantify the evolution of frictional properties from very slow, tectonic fault slip rates of millimetres per year, to those through the episodic slow slip range of millimetres per day, and into the slip rates of meters per second where earthquakes occur. Fluid pressure changes promoted by compaction and dilation during slip will also be characterized. Numerical modelling of the experiments at the laboratory scale will help to ensure that the coupled physical mechanisms involved are understood and captured in our mathematical descriptions. The large-scale behaviour of faults with the properties defined by the experiments will be explored by numerical modelling at the scale of natural faults. The numerical modelling will relate the experimental findings to field observations of episodic slow slip and earthquake nucleation and investigate the role of spatial variations in fault properties on the occurrence of episodic slow slip events vs. earthquakes. A key deliverable for this work would be identification of the range of fault conditions and physical mechanisms under which episodic slow slip, fault creep, or earthquakes can occur, leading ultimately to improved seismic hazard forecasting.

Humans have influenced the evolution of Earth's climate in many ways, the most dramatic of which has been the burning of fossil fuels and the subsequent emission of carbon dioxide (CO2) and other greenhouse gases. We know from ship-borne measurements that the ocean has provided a sink for a significant fraction of this anthropogenic carbon over the past 200 years, subsequently preventing a larger-than-observed increase in atmospheric CO2. CO2 over continents is also released by biospheric respiration, and is taken up by photosynthesis. The magnitude and spatial and temporal variability of these continental biospheric sources and sinks of CO2, and how they respond to changes in climate, is not well understood. A better quantitative understanding of the controls on biospheric continental CO2 fluxes is essential to reduce uncertainty of the human contribution to climate. Much of what we understand about continental biospheric fluxes has been inferred from in situ data. These data are sparse in both time and space, particularly over the tropics where rainforests (e.g., the Amazon) are thought to represent a significant fraction of global CO2 fluxes. The sparseness of the in situ data over this region makes it difficult to make reliable flux estimates. In contrast, the ocean CO2 fluxes typically vary over 100s km, making it easier to estimate global fluxes from in situ data. Satellite observations of CO2, representative of regional scales, are now available from the Japanese Greenhouse gases Observing SATellite (GOSAT). These data will lead to a step-change in our current understanding of the carbon cycle, but using them presents significant challenges to the carbon cycle community. The data are not straightforward to interpret, representing a measurement of CO2 absorption in the near-infra red portion of the electromagnetic spectrum. Processing the hundreds of thousands of observations per day also represents a significant technical challenge. In previous work we developed an efficient processing tool to infer CO2 sources and sinks from the satellite data and tested it using realistic simulated data. Here, we propose to assess our tool with real data from the GOSAT satellite, in collaboration with the Japanese science teams. First, careful and extensive ground-truthing of our computer simulation of atmospheric CO2 is required because it will be used to interpret the observed distributions of CO2 from GOSAT. At the same time, with progressively better knowledge of how the instrument is performing in space the GOSAT CO2 product will be improved. Second, once we develop confidence in our computer simulation and the data, we will use our processing tool to calculate some of the first CO2 flux maps inferred from satellite data. We anticipate that even our early results will help to improve mitigation strategies and reduce uncertainty in estimate future climate.

The West Antarctic Ice Sheet contains enough ice to cause 3.3 meters of sea level rise. The ice streams of its Amundsen Sea sector, which alone could contribute up to 1.2 meters of sea level rise, are thinning faster than in any other region on earth, and have the potential for rapid collapse due to inland-deepening bedrock. Using a combination of novel inverse modelling, a comprehensive ice-sheet model, and remote sensing we will: 1) Estimate the present state of the critical Amundsen sector 2) Predict its future behaviour 3) Quantify the uncertainty of these estimates and predictions The physics of ice-sheet retreat is qualitatively understood, but the detailed behaviour is dependent upon a very large number of parameters that cannot be measured directly (e.g, spatially-varying basal traction and ice stiffness). However, numerical ice sheet models have now evolved to the point where a number of relevant physical processes, such as grounding line movement and ice-sheet response to ocean forcing, can be represented accurately. Moreover, the satellite-observational record continues to grow, creating opportunities for assimilation of this new data into models. Such a model-data synthesis can allow key underlying and hidden physical parameters to be determined, facilitating data-driven prediction of future ice-sheet contribution to sea levels. However, techniques for the assimilation of data using ice sheet models remain at an early stage. A considerable amount of data remains unused and fundamental questions, such as the specific information required for reliable predictions, remain unanswered. Moreover, model simulations of future behaviour of ice sheets generally do not account for the uncertainty inherent in estimates of hidden parameters, which can potentially grow with forecast horizons. Accounting for these uncertainties is vital so that informed risk and cost-benefit analyses of sea-level rise protection and adaptation can be carried out. In the proposed project we will develop a model-based framework which will efficiently assimilate the data record for the Amundsen sector (Fig. 1), providing estimates of key physical quantities, and predictions of future behaviour. Crucially, measures of uncertainty will be provided for the estimate and predictions. We will further study the impact that different observations have on our model predictions and uncertainty therein, providing information that will be of value to future observational campaigns. While the Amundsen region is chosen as a focus in the interest of critical relevance and timeliness, the methodology can be applied more generally in other regions of Antarctica, or Greenland.

Modern physics explains a stunning variety of phenomena from the smallest of scales to the largest and has already revolutionized the world! Lasers, semi-conductors, and transistors are at the core of our laptops, cellphones, and medical equipment. And every year, new novel quantum technologies are being developed within the National Quantum Technology Programme in the UK and throughout the world that impact our everyday life and the fundamental physics research that leads to new discoveries. Quantum states of light have recently improved the sensitivity of gravitational-wave detectors, whose detections to date have enthralled the public, and superconducting transition-edge-sensors are now used in astronomy experiments that make high-resolution images of the universe. Despite the successes of modern physics, several profound and challenging problems remain. Our consortium will use recent advances in quantum technologies to address two of the most pressing questions: (i) what is the nature of dark matter and (ii) how can quantum mechanics be united with Einstein's theory of relativity? The first research direction is motivated by numerous observations which suggest that a significant fraction of the matter in galaxies is not directly observed by optical telescopes. This mysterious matter interacts gravitationally but does not seem to emit any light. Understanding the nature of dark matter will shed light on the history of the universe and the formation of galaxies and will trigger new areas of research in fundamental and possibly applied physics. Despite its remarkable importance, the nature of dark matter is still a mystery. A number of state-of-the-art experiments world-wide are looking for dark matter candidates with no luck to date. The candidate we propose to search for are axions and axion-like-particles (ALPs). These particles are motivated by outstanding questions in particle physics and may account for a significant part, if not all, of dark matter. First, we propose an experiment which will rely on quantum states of light and will detect a dark matter signal or improve the existing limits on the axion-photon coupling by a few orders of magnitude for a large range of axion masses. Second, we will build a quantum sensor which will improve the sensitivity of the international 100-m long ALPS detector of axion-like-particles by a factor of 3 - 10. Our second line of research is devoted to the nature of space and time. Recent announcements of Google's Sycamore quantum computer and the detection of gravitational waves have provided additional evidence to the long list of successful experimental tests of quantum mechanics and Einstein's theory of relativity. But how can gravity be united with quantum mechanics? To seek answers that inform this question, we propose to study two quantum aspects of space-time. First, we will experimentally investigate the holographic principle, which states that the information content of a volume can be encoded on its boundary. We will exploit quantum states of light and build two ultra-sensitive laser interferometers that will investigate possible correlations between different regions of space with unprecedented sensitivity. Second, we will search for signatures of semiclassical gravity models that approximately solve the quantum gravity problems. We will build two optical interferometers and search for the first time for signatures of semiclassical gravity in the motion of the cryogenic silicon mirrors. Answering these challenging questions of fundamental physics with the aid of modern quantum technologies has the potential to open new horizons for physics research and to reach a new level of understanding of the world we live in. The proposed research directions share the common technological platform of quantum-enhanced interferometry and benefit from the diverse skills of the researchers involved in the programme.