Palaeomagnetic recordings in ancient rocks and meteorites hold the key to answering some of the most fundamental questions in Earth Sciences. Theories regarding the evolution of the geodynamo, the thermal evolution of the Earth's core, plate tectonics and palaeogeography, and the formation of the solar system, are all constrained by observations of the ancient fields trapped in rocks that are hundreds or even thousands of millions of years old. However, not all palaeomagnetic observations are reliable, because the magnetic signal carried by most rocks and meteorites is dominated by a poorly understood thermoremanent magnetisation (TRM) in grains with non-uniform magnetic structures. Most palaeomagnetic interpretations are based on the assumption that such TRMs are carried by magnetically uniform, single domain (SD) particles, whose behaviour is well described by Néel's SD TRM theories. However, slightly larger grains with non-uniform magnetic structures are ubiquitous in nature. These are termed pseudo-SD (PSD) as they display some characteristics to SD grains (such as a large magnetic remanence), but can have a significantly different recording fidelity. Presently there is no physical model for PSD TRM acquisition therefore we have no means of assessing the stability and reliability of many palaeomagnetic signals. This proposal will address the urgent need to quantify the fundamental behaviour of PSD TRM. In particular we aim to address two key issues that can affect palaeomagnetic fidelity: (a) PSD stability as a function of time and temperature, and (b) their TRM dependence on cooling rates. This will be achieved by developing a three-dimensional numerical model that incorporates the effects of thermal-fluctuations. It will then be possible to model PSD TRM acquisition and assess the accuracy with which PSD domain states can record a geomagnetic field. A key aspect of the numerical modelling is validation of the predicted domain structures, as a function of grain size and temperature, against direct nano-metric-scale experimental observations. This will be achieved using a remarkable set of highly characterised artificial samples (produced by an electron lithography process in a previous NERC-funded study) and using the advanced transmission electron microscope (TEM) technique of off-axis electron holography, which is able to image the magnetisation on a nano-metric scale. Experiments will also be conducted on bulk samples, including a suite of already collected lavas. Once validated, the numerical model will be used to explore the fidelity of TRM recordings and palaeointensity (ancient geomagnetic field intensity) determinations in a range of grain geometries applicable to natural samples containing PSD domain states. The research will result in a comprehensive understanding of TRM acquisition for PSD grains of magnetite, which are thought to the dominant carrier of palaeomagnetic recordings, and identify how accurately PSD grains can record the ancient field. The predictive micromagnetic model we develop will be able to directly address a number of key issues, for example: (1) Palaeointensity estimates from PSD magnetites are used to constrain models of the Earth's core dynamics and the Solar System's formation. We will be able to determine whether these palaeointensities are likely to under or over estimate the true value of the ancient field. (2) Archaen palaeointensity estimates are often determined from PSD magnetite crystals, embedded with in single-silicate crystals extracted from gabrros. The model will allow us to quantify the effect of long-term cooling-rates on TRM intensity, something which cannot be done experimentally. With increased accuracy of palaeomagnetic observations, a much clearer picture will emerge of the past behaviour of the geomagnetic field, and hence a far better hope of unravelling the true nature of the early universe and the evolution and behaviour of the Earths deep interior.

The lead zirconate titanate (Pb(Zr,Ti)O3) system displays a fascinating range of structures and behaviours, but with the common feature that all compositions contain exhibit permanent electric polarisation at room temperature as a result of antiparallel displacements of the oxygen anions and the metal cations. At the PbZrO3 end of the composition range, the electric dipoles are arranged in stripes of antiparallel polarisation resulting in zero net polarisation, this is referred to as an antiferroelectric state. In contrast to this, for Pb(Zr[0.9],Ti[0.1])O3, polarisation all lies along the same direction resulting in a finite permanent macroscopic polarisation - a ferroelectric state. Just doping this latter composition with 2-4% La puts this into a slightly confused state, very much on the edge between ferroelectric and antiferroelectric ordering. Whilst it is well known that the crystal structure for this state has a large unit cell, which is incommensurate (i.e. it doesn't quite stack up as being made of a simple whole number of atomic stackings), the details of this structure are not at all well understood. The reasons for this are straightforward: it is big and not perfectly ordered (previous studies show frequent deviations from perfect order) and thus techniques like diffraction with X-rays or neutrons will have difficulties. Whilst some information can be inferred from conventional electron microscopy and diffraction (which has already been done by the applicant), the most straightforward way to solve the structure would be to be able to see where all the atoms are. This is now possible due to advances in aberration corrected electron microscopy. Recent developments have made it possible to compensate for the imperfections present in all electromagnetic lenses and this now allows us to resolve objects well below 1 + - a suitable scale for resolving atoms. The project partners at Jlich are world leaders in applying this to materials and have particular experience with doing such studies on perovskite oxides and in measuring electrical polarisation from imaging the oxygen and the metal cations in these structures. This project will allow the applicant with his prior experience of incommensurate antiferroelectrics to travel to Jlich and collaborate with them on imaging these fascinating materials at sub-+ngstrm resolution and in combination with data processing and image simulation to enable us to be able to determine the oxygen and cation displacements across the unit cell. As well as solving the structure of this interesting phase, it will also enable us to better understand its relationship to both the ideal antiferroelectric phase of PbZrO3 and to the rhombohedral ferroelectric phase of Pb(Zr[0.9],Ti[0.1])O3, and will prepare the ground for future studies of field induced transformations between antiferroelectric and ferroelectric phases.

This proposal is to develop and deploy for the first time lightweight low cost (disposable) multi-species chemical sondes to address limitations in composition measurement capability in the troposphere and low stratosphere. The sondes would incorporate state of the art CO, O3 and CO2 sensors developed by the applicants, and would be launched on standard meteorological balloons flown by National Weather Services (thus providing T, P, RH). The intention is that the sonde be suitable for use in global sonde networks such as SHADOZ and GRUAN as well as for stand-alone use, with applicability to both short term case studies (e.g. transport, chemical processes) and long term monitoring (for example linked to trend detection and climate change). The project will be in four phases: - Development and construction: involving integration of chemical sensors into a sensor module and its interface with the existing Vaisala RS92 and the new RS41 radiosonde systems. - Testing and validation: to be carried out in the JOSIE atmospheric simulation chamber, on simultaneous flights with conventional ozone sondes and in parallel with flights by the NERC FAAM research aircraft. - Field deployment: to be conducted as a) an intensive field activity as part of a larger measurement campaign, and b) regular measurement for 12-18 months. These deployments will be in Malaysia and will be used in studies of the tropical atmosphere. - Data analysis: statistical analysis of composition profiles and comparisons with the NAME and UKCA models to study chemical and transport processes in the tropical tropopause layer (TTL) and the transport of constituents in the free troposphere over Southeast Asia. We have, together with our project partners, the expertise and knowledge to develop and prove these new composition sondes which have the potential to revolutionise atmospheric measurement programmes through their ability to be launched routinely by operational meteorological agencies with minimum infrastructure.

In the 20th century plastics became an indispensable part of modern life. Most plastic products are produced by melting polymer materials and moulding them into different shapes. The flow or rheological behaviour of molten polymers is highly sensitive to their molecular architectures and molecular weight distributions. Presence of a small amount of long chain branching structures in commercial polymers can alter their rheological and thus processing properties significantly. Therefore a thorough understanding of the relationship between polymer branching and rheology is of crucial importance to the multi-billion pounds plastics industry. The dominant contributions in defining this relationship come from two respects: entanglement effects among long polymer chains or branches and complexity in branching architectures. The entanglement effects originate from the fact that long polymer chains can not pass through each other. As a consequence, the lateral motion of the chains are suppressed, leading to the extremely long relaxation time and characteristic viscoelastic behaviour of entangled polymers, which are qualitatively different from the viscous behaviour of fast relaxing simple liquids. Theoretical works on entanglement dynamics have been for 40 years primarily based on the tube theory. This model assumes that the motion of a linear polymer chain is restricted to a tube-like region along its contour formed by surrounding chains, similar to a snake slithering through an array of obstacles. Recent tube theories can provide appropriate description of the linear rheology of monodisperse linear polymers, but is facing serious difficulties in describing the branched polymers. Synthesized branched polymers can have various architectures, such as star, H-shaped, comb and Cayley-tree polymers. The commercial polymers, such as metallocene polyethylene resins, can even have branches on branches, i.e., hyperbranching, structures. The branching structures prevent these polymers from sliding in the melt as do the linear chains. Instead a star polymer diffuses by retracting its arms all the way to the branch point, allowing this point to move a short distance, and then stretching out the arms again. This is analogous to an octopus entangled in an array of topological constraints (e.g., a fishing net). The relaxation time of stars thus grows exponentially with the length of the arms, in radical contrast to the power law chain-length dependence of the linear polymers. Polymers with more complicated architectures are assumed to relax in a hierarchical way. The relaxation starts from the retraction of the outermost branch arms and proceeds to inner segments layer by layer till the core of the molecule. Theoretical modelling of the branched polymers needs to address several essential questions including the dynamics of the branch arm retraction, the branch point diffusion and the hierarchical relaxation, as well as the reduced entanglement effects caused by the relaxation of surrounding polymers. The fast grow in computer power and simulation techniques enables us to examine these problems in great details. In this project, we propose to perform molecular dynamics simulations to investigate the relaxation dynamics of model branched polymers at the microscopic level. Special attention will be paid to examine and, if needed, re-formulate the assumptions and analytical expressions used in the current tube theories for describing the above-mentioned dynamic processes. Based on these microscopic understanding, more coarse-grained theoretical models will be developed, which will ultimately allow prediction of dynamics and rheology of general mixtures of branched polymers with arbitrary architectures over many decades of time and length scales.

How did dust and gas produce a planet capable of supporting life? This is one of the most fundamental of questions, and engages everyone from school children to scientists. Our planet formed 4.5 billion years ago along with the Sun and the other planets and minor bodies in our Solar System, and it is the only habitable world yet discovered on which life evolved. By understanding the details of how our Solar System formed we can hope to find an answer. We now know much about how stars and their accompanying planetary systems form in general. We know that stars form by the collapse of interstellar clouds of dust and gas. Planets are constructed in disks known as planetary nebula formed by the rotation of the collapsing gas cloud. It was in the solar nebula, surrounding the young Sun, that all the objects in our Solar System were created through a process called accretion. There is, however, a long list of details we don't know about how our Solar System formed. Why, for example, are all the planets so different? Why is Venus an inferno with a thick carbon dioxide atmosphere, Mars a frozen rock with a thin atmosphere, and Earth a haven for life? The answer lies in events that predated the assembly of these planets, it lies in the early history of the nebula and the events that occurred as fine-dust stuck together to form larger objects known as planetesimals, and as those planetesimals changed through collisions, heating and the effects of water to become the building blocks of planets. Our research intends to follow the evolution of planetary materials from the sources of dust prior to solar system formation, through the assembly of precursor objects within the solar nebula to the alteration of these objects as they became planets. The source of presolar dust provides a context to our solar system. From what types of star was dust derived and how did dust from these different sources mix and change in the solar nebula? These questions can be answered by analysis of isotopes of high temperature, refractory elements, within meteorites - rocks from asteroids that preserve a history of the early solar system. Meteorites, together with cosmic dust particles, also retain the fine-dust particles from the solar nebula. These dust grains are smaller than a millionth of a metre but modern microanalysis can expose their minerals and compositions. We will study the fine-grained components of meteorites and cosmic dust to investigate how fine-dust began accumulating in the solar nebula, how heating by an early hot nebula and repeated short heating events affected aggregates of dust grains, and whether magnetic fields helped control the distribution of dust in the solar nebula. In addition to the rocky and metallic materials that make up the planets, our research will examine the fate of organic materials that were crucial to the origins of life. Through newly developed methods we can trace this history of organic matter in meteorites from their formation in interstellar space, through the solar nebula and into planetesimals. This research will examine the effect of events also recorded in rocky and metallic fine-dust on the organic components of the early planetary materials from which the first living things on Earth were constructed. Once the planets finally formed, their materials continued to change. Our research focuses on the planet Mars, which provides a second example of a planetary body on which life could have appeared. We will trace the evolution of water and organics from planetary formation to the present day. Research on landforms on Mars will examine a crucial period in the planet's history, when global climate change transformed the planet into an arid wasteland, to evaluate the opportunity for organisms to adapt and survive. Research on the survival or organic compounds in martian soil will test whether the signature of life can still be detected on the planet.