Cartan's spiral staircase in physics and, in particular, in the gauge theory of dislocations

In 1922, Cartan introduced in differential geometry, besides the Riemannian curvature, the new concept of torsion. He visualized a homogeneous and isotropic distribution of torsion in three dimensions (3d) by the "helical staircase", which he constructed by starting from a 3d Euclidean space and by defining a new connection via helical motions. We describe this geometric procedure in detail and define the corresponding connection and the torsion. The interdisciplinary nature of this subject is already evident from Cartan's discussion, since he argued - but never proved - that the helical staircase should correspond to a continuum with constant pressure and constant internal torque. We discuss where in physics the helical staircase is realized: (i) In the continuum mechanics of Cosserat media, (ii) in (fairly speculative) 3d theories of gravity, namely a) in 3d Einstein-Cartan gravity - this is Cartan's case of constant pressure and constant intrinsic torque - and b) in 3d Poincare gauge theory with the Mielke-Baekler Lagrangian, and, eventually, (iii) in the gauge field theory of dislocations of Lazar et al., as we prove for the first time by arranging a suitable distribution of screw dislocations. Our main emphasis is on the discussion of dislocation field theory.Comment: 31 pages, 8 figure

A proof of uniqueness of the Gurarii space

We present a short and elementary proof of isometric uniqueness of the Gurarii space.Comment: 6 pages, some improvements incorporate

Genomic reconstruction of a novel, deeply branched sediment archaeal phylum with pathways for acetogenesis and sulfur reduction

Marine and estuary sediments contain a variety of uncultured archaea whose metabolic and ecological roles are unknown. De novo assembly and binning of high-throughput metagenomic sequences from the sulfate–methane transition zone in estuary sediments resulted in the reconstruction of three partial to near-complete (2.4–3.9 Mb) genomes belonging to a previously unrecognized archaeal group. Phylogenetic analyses of ribosomal RNA genes and ribosomal proteins revealed that this group is distinct from any previously characterized archaea. For this group, found in the White Oak River estuary, and previously registered in sedimentary samples, we propose the name ‘Thorarchaeota'. The Thorarchaeota appear to be capable of acetate production from the degradation of proteins. Interestingly, they also have elemental sulfur and thiosulfate reduction genes suggesting they have an important role in intermediate sulfur cycling. The reconstruction of these genomes from a deeply branched, widespread group expands our understanding of sediment biogeochemistry and the evolutionary history of Archaea

Order parameter oscillations in Fe/Ag/Bi2Sr2CaCu2O{8+delta} tunnel junctions

We have performed temperature dependent tunneling conductance spectroscopy on Fe/Ag/Bi2Sr2CaCu2O8 (BSCCO) planar junctions. The multilayered Fe counterelectrode was designed to probe the proximity region of the ab-plane of BSCCO. The spectra manifested a coherent oscillatory behavior with magnitude and sign dependent on the energy, decaying with increasing distance from the junction barrier, in conjunction with the theoretical predictions involving d-wave superconductors coupled with ferromagnets. The conductance oscillates in antiphase at E = 0 and E = +/-Delta. Spectral features characteristic to a broken time-reversal pairing symmetry are detected and they do not depend on the geometrical characteristics of the ferromagnetic film.Comment: 4 pages and 4 figures Submitted to Physical Review Letter

Choices:Future trade-offs and plausible pathways

Policy development and management of deltas in the Anthropocene involves the consideration of trade-offs and the balancing of positive and negative consequences for delta functions and the societies that rely on them. This assessment outlines policy-driven and spatial trade-offs that dominate the landscape of choice. It highlights examples of such trade-offs using plausible delta futures and the governance choices associated with them. The analysis is based on modelling broad-scale processes and individual adaptive actions. It highlights how policy choices to maximise economic growth can, for example, have unforeseen consequences such as diminished well-being for some populations. Hence the chapter concludes that trade-offs are a crucial governance challenge for future sustainability of deltas

Identification of linear and nonlinear sensory processing circuits from spiking neuron data

Inferring mathematical models of sensory processing systems directly from input-output observations, while making the fewest assumptions about the model equations and the types of measurements available, is still a major issue in computational neuroscience. This letter introduces two new approaches for identifying sensory circuit models consisting of linear and nonlinear filters in series with spiking neuron models, based only on the sampled analog input to the filter and the recorded spike train output of the spiking neuron. For an ideal integrate-and-fire neuron model, the first algorithm can identify the spiking neuron parameters as well as the structure and parameters of an arbitrary nonlinear filter connected to it. The second algorithm can identify the parameters of the more general leaky integrate-and-fire spiking neuron model, as well as the parameters of an arbitrary linear filter connected to it. Numerical studies involving simulated and real experimental recordings are used to demonstrate the applicability and evaluate the performance of the proposed algorithms

Subpopulation Treatment Effect Pattern Plot (STEPP) Methods with R and Stata

We introduce the stepp packages for R and Stata that implement the subpopulation treatment effect pattern plot (STEPP) method. STEPP is a nonparametric graphical tool aimed at examining possible heterogeneous treatment effects in subpopulations defined on a continuous covariate or composite score. More pecifically, STEPP considers overlapping subpopulations defined with respect to a continuous covariate (or risk index) and it estimates a treatment effect for each subpopulation. It also produces confidence regions and tests for treatment effect heterogeneity among the subpopulations. The original method has been extended in different directions such as different survival contexts, outcome types, or more efficient procedures for identifying the overlapping subpopulations. In this paper, we also introduce a novel method to determine the number of subjects within the subpopulations by minimizing the variability of the sizes of the subpopulations generated by a specific parameter combination. We illustrate the packages using both synthetic data and publicly available data sets. The most intensive computations in R are implemented in Fortran, while the Stata version exploits the powerful Mata language

HATS-17b: A Transiting Compact Warm Jupiter in a 16.3 Days Circular Orbit

We report the discovery of HATS-17b, the first transiting warm Jupiter of the HATSouth network. HATS-17b transits its bright (V=12.4) G-type (M$_{\star}$=1.131 $\pm$ 0.030 M$_{\odot}$, R$_{\star}$=1.091$^{+0.070}_{-0.046}$ R$_{\star}$) metal-rich ([Fe/H]=+0.3 dex) host star in a circular orbit with a period of P=16.2546 days. HATS-17b has a very compact radius of 0.777 $\pm$ 0.056 R$_J$ given its Jupiter-like mass of 1.338 $\pm$ 0.065 M$_J$. Up to 50% of the mass of HATS-17b may be composed of heavy elements in order to explain its high density with current models of planetary structure. HATS-17b is the longest period transiting planet discovered to date by a ground-based photometric survey, and is one of the brightest transiting warm Jupiter systems known. The brightness of HATS-17b will allow detailed follow-up observations to characterize the orbital geometry of the system and the atmosphere of the planet.Comment: 12 page, 8 figures, submitted to A