A systematic approach to the scaling and merging of data from multiple crystals in macromolecular crystallography is introduced and explained.

A 2+1 dimensional fermion field theory is proposed as a model for the lowenergy electronic excitations in monolayer graphene. The model consists of N f = 2 fourcomponent Dirac fermions moving in the plane and interacting via a contact interaction between charge densities. For strong couplings there is a continuous transition to a Mott insulting phase. We present results of an extensive numerical study of the model's critical region, including the order parameter, its associated susceptibility, and for the first time the quasiparticle propagator. The data enables an extraction of the critical exponents at the transition, including the dynamical critical exponent, which are hypothesised to be universal features of a quantum critical point. The relation of our model with others in the literature is discussed, along with the implications for physical graphene following from our value of the critical coupling.

Fast Radio Bursts (FRBs), are millisecond radio signals that exhibit dispersion larger than what the Galactic electron density can account for. We have conducted a 1446 hour survey for Fast Radio Bursts (FRBs) at 145 MHz, covering a total of 4193 sq. deg on the sky. We used the UK station of the LOFAR radio telescope -the Rawlings Array -, accompanied for a majority of the time by the LOFAR station at Nançay, observing the same fields at the same frequency. Our real-time search backend, ARTEMIS, utilizes graphics processing units to search for pulses with dispersion measures up to 320 cm −3 pc. Previous derived FRB rates from surveys around 1.4 GHz, and favoured FRB interpretations, motivated this survey, despite all previous detections occurring at higher dispersion measures. We detected no new FRBs above a signal-to-noise threshold of 10, leading to the most stringent upper limit yet on the FRB event rate at these frequencies: 29 sky −1 day −1 for 5 ms-duration pulses above 62 Jy. The non-detection could be due to scatter-broadening, limitations on the volume and time searched, or the shape of FRB flux density spectra. Assuming the latter and that FRBs are standard candles, the non-detection is compatible with the published FRB sky rate, if their spectra follow a power law with frequency (∝ ν α ), with α +0.1, demonstrating a marked difference from pulsar spectra. Our results suggest that surveys at higher frequencies, including the low frequency component of the Square Kilometre Array, will have better chances to detect, estimate rates and understand the origin and properties of FRBs.

The vector meson mass is extracted from a large sample of partially quenched, two-flavor lattice QCD simulations. For the first time, discretisation, finite-volume and partial quenching artefacts are treated in a unified framework which is consistent with the low-energy behaviour of QCD. This analysis incorporates the leading infrared behaviour dictated by chiral effective field theory. As the two-pion decay channel cannot be described by a low-energy expansion alone, a highly-constrained model for the decay channel of the rho-meson is introduced. The latter is essential for extrapolating lattice results from the quark-mass regime where the rho is observed to be a physical bound state.Recent developments in lattice QCD have enabled the first large-scale simulation of chiral, dynamical fermions [1]. While this accomplishment is a significant milestone in the progress towards an accurate description of physical QCD, the high demand on computing resources restricts practical calculations to an unphysical domain of simulation parameters. In particular, lattice QCD involves a discretised space-time of finite spatial extent, with input quark masses much larger than those in Nature. Each of these approximations requires special attention in the extraction of physical observables from Monte Carlo simulations. In this Letter we analyse a very large set of partially quenched data for the mass of the ρ meson. We show that a systematic analysis of this data enables us to remove the effects of partial quenching and to take both the continuum and infinite volume limits. The resulting data lies on a single, well defined curve which extrapolates to a value within ∼1% of the physical ρ mass. The contrast between the raw lattice data (note the scatter in Fig. 2) and the corrected data shown in Fig. 3 is striking.