Triangle-free intersection graphs of line segments with large chromatic number

In the 1970s, Erdos asked whether the chromatic number of intersection graphs of line segments in the plane is bounded by a function of their clique number. We show the answer is no. Specifically, for each positive integer $k$, we construct a triangle-free family of line segments in the plane with chromatic number greater than $k$. Our construction disproves a conjecture of Scott that graphs excluding induced subdivisions of any fixed graph have chromatic number bounded by a function of their clique number.Comment: Small corrections, bibliography updat

Nanoscale magnetometry through quantum control of nitrogen-vacancy centres in rotationally diffusing nanodiamonds

The confluence of quantum physics and biology is driving a new generation of quantum-based sensing and imaging technology capable of harnessing the power of quantum effects to provide tools to understand the fundamental processes of life. One of the most promising systems in this area is the nitrogen-vacancy centre in diamond - a natural spin qubit which remarkably has all the right attributes for nanoscale sensing in ambient biological conditions. Typically the nitrogen-vacancy qubits are fixed in tightly controlled/isolated experimental conditions. In this work quantum control principles of nitrogen-vacancy magnetometry are developed for a randomly diffusing diamond nanocrystal. We find that the accumulation of geometric phases, due to the rotation of the nanodiamond plays a crucial role in the application of a diffusing nanodiamond as a bio-label and magnetometer. Specifically, we show that a freely diffusing nanodiamond can offer real-time information about local magnetic fields and its own rotational behaviour, beyond continuous optically detected magnetic resonance monitoring, in parallel with operation as a fluorescent biomarker.Comment: 9 pages, with 5 figure

SESAME: exploring small businesses' behaviour to enhance resilience to flooding

In the United Kingdom, small and medium sized enterprises (SMEs) account for approximately 99.9% of businesses, 60% of the working population and 47% annual turnover. However, despite the important contribution that SMEs make to the economy, this size of business remains under-researched with a significant gap in understanding how the disruption caused by flooding impacts on SMEs from the time at which a flood event occurs through to the 'return' to normal operations. Business continuity management is a recognised approach for enhancing organisational resilience to major disruptions (ISO 22301, 2012). However, this strategic approach to building such resilience in SMEs is under-explored in the literature with a limited range of empirical data to draw on. This paper presents an overview of an inter-disciplinary research project funded by the UK's Engineering and Physical Science Research Council, called SESAME, which examines SMEs' operational response and preparedness to flooding. Furthermore, SESAME consists of four stands of research which bring together a number of disciplines including agent based modelling and simulation, flood modelling, business continuity management, economic modelling and behavioural science. This paper provides an overview of the different research stands within the SESAME project aimed at enhancing SMEs' resilience to flooding

Quasi-Particle Spectra, Charge-Density-Wave, Superconductivity and Electron-Phonon Coupling in 2H-NbSe2

High-resolution photoemission has been used to study the electronic structure of the charge density wave (CDW) and superconducting (SC) dichalcogenide, 2H- NbSe2. From the extracted self-energies, important components of the quasiparticle (QP) interactions have been identified. In contrast to previously studied TaSe2, the CDW transition does not affect the electronic properties significantly. The electron-phonon coupling is identified as a dominant contribution to the QP self-energy and is shown to be very anisotropic (k-dependent) and much stronger than in TaSe2.Comment: 4 pages, 3 figures, minor changes, to appear in PR

An angle-resolved soft x-ray spectroscopy study of the electronic states of single crystal MgB2

Angle-resolved soft x-ray measurements made at the boron K-edge in single crystal MgB2 provide new insights into the B-2p local partial density of both unoccupied and occupied band states. The strong variation of absorption with incident angle of exciting x-rays permits the clear separation of contributions from \sigma states in the boron plane and \pi states normal to the plane. A careful comparison with theory accurately determines the energy of selected critical $k$ points in the conduction band. Resonant inelastic x-ray emission at an incident angle of 15 degrees shows a large enhancement of the emission spectra within about 0.5 eV of the Fermi level that is absent at 45 degrees and is much reduced at 60 degrees. We conclude that momentum transferred from the resonant inelastic x-ray scattering (RIXS) process couples empty and filled states across the Fermi level.Comment: Accepted to PRB. 13 pages, 6 figure

A comparative analysis of pharmacists' perspectives on codeine use and misuse - a three country survey

Background: The misuse of codeine is of increasing concern in a number of countries, particularly as this relates to over -the-counter pain and cough relief medication, and is also supplied as a prescription medicine. The study aimed to obtain and analyse the opinions and experience of pharmacy staff with regard to codeine misuse. Methods: A cross-sectional web-based survey of pharmacy staff’s perspectives on this issue was administered through professional or regulatory bodies and completed by samples drawn in South Africa (n = 124), Ireland (n = 464) and the United Kingdom (n = 129). Results: The majority of participants reported combination codeine-containing products as most popular, but significantly more pharmacy staff in South Africa reported codeine-containing cough syrups as most commonly popular (X2 = 122.7(2), p < 0.001). Codeine use was also seen significantly more of a public health problem in South Africa than in the other two countries (X2 = 7.6(2), p = 0.02). There was no difference across countries in the level of codeine misuse reported by pharmacy staff. Further findings indicate that professional training and education is desired, with unequivocal findings for the need for greater codeine control (X2 = 12.0(2), p = 0.002). Conclusion: In conclusion, there were some inter-country differences, but overall the findings seem to suggest that pharmacists across all three countries view codeine misuse as a problem among their customers. Recommendations centre on risk management, surveillance and staff training