Missing Shapiro steps and the 8π8\pi-periodic Josephson effect in interacting helical electron systems

Two-particle backscattering in time-reversal invariant interacting helical electron systems can lead to the formation of quasiparticles with charge $e/2$. We propose a way to detect such states by means of the Josephson effect in the presence of proximity-induced superconductivity. In this case, the existence of $e/2$ charges leads to an $8 \pi$-periodic component of the Josephson current which can be identified through measurement of Shapiro steps in Josephson junctions. In particular, we show that even when there is weak explicit time-reversal symmetry breaking, which causes the two-particle backscattering to be a sub-leading effect at low energies, its presence can still be detected in driven, current-biased Shapiro step measurements. The disappearance of some of these steps as a function of the drive frequency is directly related to the existence of non-Abelian zero-energy states. We suggest that this effect can be measured in current state-of-the-art Rashba wires.Comment: 9 pages, 5 figures. A new submission extending and expanding our analysis in arXiv:1507.08881. (v2) References adde

Clustering-based Redshift Estimation: Comparison to Spectroscopic Redshifts

We investigate the potential and accuracy of clustering-based redshift estimation using the method proposed by M\'enard et al. (2013). This technique enables the inference of redshift distributions from measurements of the spatial clustering of arbitrary sources, using a set of reference objects for which redshifts are known. We apply it to a sample of spectroscopic galaxies from the Sloan Digital Sky Survey and show that, after carefully controlling the sampling efficiency over the sky, we can estimate redshift distributions with high accuracy. Probing the full colour space of the SDSS galaxies, we show that we can recover the corresponding mean redshifts with an accuracy ranging from $\delta$z=0.001 to 0.01. We indicate that this mapping can be used to infer the redshift probability distribution of a single galaxy. We show how the lack of information on the galaxy bias limits the accuracy of the inference and show comparisons between clustering redshifts and photometric redshifts for this dataset. This analysis demonstrates, using real data, that clustering-based redshift inference provides a powerful data-driven technique to explore the redshift distribution of arbitrary datasets, without any prior knowledge on the spectral energy distribution of the sources.Comment: 13 pages. Submitted to MNRAS. Comments welcom

Deciduous enamel 3D microwear texture analysis as an indicator of childhood diet in medieval Canterbury, England

This study conducted the first three dimensional microwear texture analysis of human deciduous teeth to reconstruct the physical properties of medieval childhood diet (age 1-8yrs) at St Gregory's Priory and Cemetery (11th to 16th century AD) in Canterbury, England. Occlusal texture complexity surfaces of maxillary molars from juvenile skeletons (n=44) were examined to assess dietary hardness. Anisotropy values were calculated to reconstruct dietary toughness, as well as jaw movements during chewing. Evidence of weaning was sought, and variation in the physical properties of food was assessed against age and socio-economic status. Results indicate that weaning had already commenced in the youngest children. Diet became tougher from four years of age, and harder from age six. Variation in microwear texture surfaces was related to historical textual evidence that refers to lifestyle developments for these age groups. Diet did not vary with socio-economic status, which differs to previously reported patterns for adults. We conclude, microwear texture analyses can provide a non-destructive tool for revealing subtle aspects of childhood diet in the past

MRAPs, Irregular Warfare, and Pentagon Reform

The controversial MRAPs raise two questions. First, does the MRAP experience support the contention that the Pentagon is not sufficiently able to field irregular warfare capabilities? Second, what factors best explain the MRAP failure, whether that failure is determined to be their delayed fielding or the fact that they were fielded at all? We conclude that MRAPs are a valid irregular warfare requirement and that the Pentagon should have been better prepared to field them, albeit not on the scale demanded by events in Iraq. We also argue that the proximate cause of the failure to quickly field MRAPs is not the Pentagon’s acquisition system but rather the requirements process, reinforced by more fundamental organizational factors. These findings suggest that acquisition reform is the wrong target for advancing Secretary Gates’ objective of improving irregular warfare capabilities, and that achieving the objective will require more extensive reforms than many realize