Development of an Open Source Connected Autonomous Rover (OSCAR) for Under Canopy Row Crop Sampling

High density sampling of row cropping systems can enable a variety of agronomic research that is currently too labor intensive to feasibly pursue by hand. While aerial drones are commonly used to collect field data, there are numerous measurements of interest that require sensors deployed under the crop canopy. This project examines the development of a robust autonomous rover (OSCAR) that can travel through rows of corn throughout the growing season. OSCAR has a 22” wheelbase with differential steering allowing it to navigate through corn rows without damaging the plants. OSCAR is equipped with an RTK GNSS module and stereo vision camera which allows it to navigate through rows autonomously. The robot’s ability to reliably navigate and avoid obstacles continues to be improved upon in simulation and in real fields

Universal Behaviour of the Superfluid Fraction and Tc of He-3 in 99.5% Open Aerogel

We have investigated the superfluid transition of He-3 in a 99.5% porosity silica aerogel. This very dilute sample shows behaviour intermediary between bulk He-3 and He-3 confined to the denser aerogels previously studied. We present data on both the superfluid transition temperature and the superfluid density and compare our results with previous measurements. Finally, we show that the suppression of the superfluid transition temperature and suppression of the superfluid density of He-3 in aerogel follow a universal relation for a range of aerogel samples.Comment: 4 pages, 5 figures; 1 new figure, minor change

Interfacing GHz-bandwidth heralded single photons with a room-temperature Raman quantum memory

Photonics is a promising platform for quantum technologies. However, photon sources and two-photon gates currently only operate probabilistically. Large-scale photonic processing will therefore be impossible without a multiplexing strategy to actively select successful events. High time-bandwidth-product quantum memories - devices that store and retrieve single photons on-demand - provide an efficient remedy via active synchronisation. Here we interface a GHz-bandwidth heralded single-photon source and a room-temperature Raman memory with a time-bandwidth product exceeding 1000. We store heralded single photons and observe a clear influence of the input photon statistics on the retrieved light, which agrees with our theoretical model. The preservation of the stored field's statistics is limited by four-wave-mixing noise, which we identify as the key remaining challenge in the development of practical memories for scalable photonic information processing

Spin susceptibility of the superfluid 3^{3}He-B in aerogel

The temperature dependence of paramagnetic susceptibility of the superfluid ^{3}He-B in aerogel is found. Calculations have been performed for an arbitrary phase shift of s-wave scattering in the framework of BCS weak coupling theory and the simplest model of aerogel as an aggregate of homogeneously distributed ordinary impurities. Both limiting cases of the Born and unitary scattering can be easily obtained from the general result. The existence of gapless superfluidity starting at the critical impurity concentration depending on the value of the scattering phase has been demonstrated. While larger than in the bulk liquid the calculated susceptibility of the B-phase in aerogel proves to be conspicuously smaller than that determined experimentally in the high pressure region.Comment: 10 pages, 4 figures, REVTe

On the supranational spell of PISA in policy

BACKGROUND: PISA results appear to have a large impact upon government policy. The phenomenon is growing, with more countries taking part in PISA testing and politicians pointing to PISA results as reasons for their reforms. PURPOSE: The aims of this research were to depict the policy reactions to PISA across a number of jurisdictions, to see whether they exhibited similar patterns and whether the same reforms were evident. SOURCES OF EVIDENCE: We investigated policy and media reactions to the 2009 and 2012 PISA results in six cases: Canada, China (Shanghai), England, France, Norway and Switzerland. Cases were selected to contrast high-performing jurisdictions (Canada, China) with average performers (England, France, Norway and Switzerland). Countries that had already been well reported on in the literature were excluded (Finland, Germany). DESIGN AND METHODS: Policy documents, media reports and academic articles in English, French, Mandarin and Norwegian relating to each of the cases were critically evaluated. RESULTS: A policy reaction of ‘scandalisation’ was evident in four of the six cases; a technique used to motivate change. Five of the six cases showed ‘standards-based reforms’ and two had reforms in line with the ‘ideal-governance’ model. However, these are categorisations: the actual reforms had significant differences across countries. There are chronological problems with the notion that PISA results were causal with regard to policy in some instances. Countries with similar PISA results responded with different policies, reflecting their differing cultural and historical education system trajectories. CONCLUSIONS: The connection between PISA results and policy is not always obvious. The supranational spell of PISA in policy is in the way that PISA results are used as a magic wand in political rhetoric, as though they conjure particular policy choices. This serves as a distraction from the ideological basis for reforms. The same PISA results could motivate a range of different policy solutions

Ultrahigh and persistent optical depths of caesium in Kagom\'e-type hollow-core photonic crystal fibres

Alkali-filled hollow-core fibres are a promising medium for investigating light-matter interactions, especially at the single-photon level, due to the tight confinement of light and high optical depths achievable by light-induced atomic desorption. However, until now these large optical depths could only be generated for seconds at most once per day, severely limiting the practicality of the technology. Here we report the generation of highest observed transient ($>10^5$ for up to a minute) and highest observed persistent ($>2000$ for hours) optical depths of alkali vapours in a light-guiding geometry to date, using a caesium-filled Kagom\'e-type hollow-core photonic crystal fibre. Our results pave the way to light-matter interaction experiments in confined geometries requiring long operation times and large atomic number densities, such as generation of single-photon-level nonlinearities and development of single photon quantum memories.Comment: Author Accepted versio

Glass state of superfluid 3He-A in aerogel

Glass states formed in the superfluid $^3$He confined in aerogel are discussed. If the short range order corresponds to the A-phase state, the glass state is nonsuperfluid in the long wave length limit. The superfluidity can be restored by application of a small mass current. Transitions between the superfluid and nonsuperfluid glass states can be triggered by small magnetic field and by the change of the tipping angle of magnetization in NMR experiments.Comment: 6 pages, LaTeX file, no figures, submitted to JETP Letter

Model of Inhomogeneous Impurity Distribution in Fermi Superfluids

The standard treatment of impurities in metals assumes a homogeneous distribution of impurities. In this paper we study distributions that are inhomogeneous. We discuss in detail the "isotropic inhomogeneous scattering model" which takes into account the spatially varying scattering on the scale of the superfluid coherence length. On a large scale the model reduces to a homogeneous medium with renormalized parameter values. We apply the model to superfluid 3He, where porous aerogel acts as the impurity. We calculate the transition temperature Tc, the order parameter, and the superfluid density. Both A- and B-like phases are considered. Two different types of behavior are identified for the temperature dependence of the order parameter. We compare the calculations with experiments on 3He in aerogel. We find that most of the differences between experiments and the homogeneous theory can be explained by the inhomogeneous model. All our calculations are based on the quasiclassical theory of Fermi liquids. The parameters of this theory for superfluid 3He in aerogel are discussed.Comment: 14 pages, 9 figures, minor change