'Discovery'). No activity had been detected at the same location in the images taken on the previous night and earlier, indicating that the SN likely exploded between May 2.29 and 3.29. Our follow-up spectroscopic campaign (See Extended Data Table 1 for the observation log) established that iPTF14atg was a Type Ia supernova (SN Ia). 3Upon discovery we triggered observations with the Ultraviolet/Optical Telescope (UVOT) and the X-ray Telescope (XRT) onboard the Swift space observatory 11 (observation and data reduction is detailed in Methods subsection 'Data acquisition'; raw measurements are shown in Extended Data Table 2). As can be seen in Figure 1, the UV brightness of iPTF14atg declined substantially in the first two observations. A rough energy flux measure in the UV band is provided by ν f ν ≈ 3×10 −13 ergs cm −2 s −1 in the uvm2 band. Starting from the third epoch, the UV and optical emission began to rise again in a manner similar to that seen in other SNe Ia. The XRT did not detect any X-ray signal at any epoch (Methods subsection 'Data acquisition'). We thus conclude that iPTF 14atg emitted a pulse of radiation primarily in the UV band. This pulse with an observed luminosity of L UV ≈ 3×10 41 ergs s −1 was probably already declining by the first epoch of the Swift observations (within four days of its explosion).Figure 1 also illustrates that such an early UV pulse from a SN Ia within four days of its explosion is unprecedented 12,13 . We now seek an explanation for this early UV emission.As detailed in Methods subsection 'Spherical models for the early UV pulse', we explored models in which the UV emission is spherically symmetric with the SN explosion (such as shock cooling and circumstellar interaction). These models are unable to explain the observed UV pulse. Therefore we turn to asymmetric models in which the UV emission comes from particular directions.A reasonable physical model is UV emission arising in the ejecta as the ejecta encounters a companion 9,14 . When the rapidly moving ejecta slams into the companion, a strong 4 reverse shock is generated in the ejecta that heats up the surrounding material. Thermal radiation from the hot material, which peaks in the ultraviolet, can then be seen for a few days until the fast-moving ejecta engulfs the companion and hides the reverse shock region. We compare a semi-analytical model 9 to the Swift/UVOT lightcurves. For simplicity, we fix the explosion date at May 3. We assume that the exploding white dwarf is close to the Chandrasekhar mass limit (1.4 solar mass) and that the SN explosion energy is 10 51 ergs. These values lead to a mean expansion velocity of 10 4 km s −1 for the ejecta. Since the temperature at the collision location is so high that most atoms are ionized, the opacity is probably dominated by electron scattering. To further simplify the case, we assume that the emission from the reverse shock region is blackbody and isotropic. In order to explain the UV lightcurves, the companion star should be located 60 solar radii away from the w...

The total 'Be(n, p)'Li cross section has been measured from 25 meV to 13.5 keV. These energies correspond to temperatures of T =2.9)& 10 ' to 0.16 GK. For thermal neutrons the cross sections to the ground state (po) and the first excited state (p, ) of 'Li are 38400+800 b and 4202120 b, respectively. This result for the total 'Be(n, p)'Li thermal cross section is about 25%%uo lower, and is approximately a factor of 10 more precise than previous published measurements. For energies above 100 eV, a significant departure from a 1/u shape for the total cross section is observed. The data were analyzed using a single-level approximation, and were also analyzed together with other data using multilevel-multichannel R-matrix theory. Results are presented for the properties of the 2 threshold state and for a possible nearby 2 state. The astrophysical reaction rate, N~(nv ), was calculated from the measured cross sections for the combined po and pl transitions. The resulting reaction rate is approximately 60-80% of the rate currently in use. This reduction in the Be(n,p) Li reaction rate could result in a calculated increase in the production of 'Li during the big bang by as much as 20%.

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Electrical capacitance tomography (ECT) is used to characterise a fluidised bed. Here, ECT measurements are reconstructed by penalising the Total Variation. Algorithm permits characterisation of regions with sharp changes in permittivity. ECT measurements of the bubble size are compared with existing correlations. a b s t r a c tElectrical capacitance tomography (ECT) provides a means for non-invasively imaging multiphase flows, such as those in fluidised beds. Traditionally ECT images are reconstructed using the assumption that the distribution of permittivity varies smoothly throughout the sensor region. However, for many applications there are step changes in the permittivity, for example, between the bubble and particulate phases in a fluidised bed, and the assumption of smoothness is flawed. In this article a Total Variation Iterative Soft Thresholding (TV-IST) algorithm is used to reconstruct ECT images that allows for sharp transitions in the permittivity distribution. This new algorithm has been compared with established algorithms for ECT image reconstruction. It was found that the TV-IST algorithm reduced the sensitivity to the threshold level chosen when extracting measurements of bubble size from ECT data sets. Measurements of the bubble size distribution in the fluidised bed using the TV-IST algorithm agreed closely with established empirical correlations for the size of bubbles. The results demonstrate that ECT can provide accurate and high spatial resolution measurements of features such as bubbles in gas-solid fluidised beds.