Streamlined Subglacial Bedform Sensitivity to Bed Characteristics Across the Deglaciated Northern Hemisphere

Streamlined subglacial bedforms observed in deglaciated landscapes provide the opportunity to assess the sensitivity of glacier dynamics to bed characteristics across broader spatiotemporal scales than is possible for contemporary glacial systems. While many studies of streamlined subglacial bedforms rely on manual mapping and qualitative (i.e., visual) assessment, we semi-automatically identify 11,628 sedimentary and bedrock bedforms, created during and following the Last Glacial Maximum across nine geologically and topographically diverse deglaciated sites in the Northern Hemisphere. Using this large dataset of landforms and associated morphometrics, we empirically test the importance of subglacial terrain on bedform morphology and ice-flow behavior. A minimum bedform length–width ratio threshold provides a constraint on minimum morphometrics needed for streamlined bedforms to develop. Similarities in bedform metric distribution regardless of bed properties indicate that all bed types may support similar distributions of warm-based ice flow conditions. Ice flow within valleys with easily erodible beds host the most elongate bedforms yet the widest range in bedform elongation and bedform surface relief. The presence of these highly elongate bedforms suggest high ice-flow velocities occur within valley settings despite spatially heterogeneous landform-generating processes. In contrast, lithified sedimentary beds within regions not constrained by topography on the scale of 1–102 km contain bedforms with high density and packing, low change in surface relief and low elongation, indicating spatially uniform and organized interactions at the ice–bed interface and consistency in ice-flow velocity. Regardless of genesis, we find a sensitivity of bedform elongation (i.e., used to interpret ice-flow speed or persistence) to topographic conditions on the scale of 1–102 km, while bedform density is sensitive to bed lithology. The findings presented in this study provide analogues for processes of subglacial erosion and deposition, ice–bed interactions and warm-based ice flow within contemporary glacial systems

Relación entre la fertilización con azufre y el suministro de nitrógeno para Trébol y Ryegrass.

Se realizó un estudio de invernadero con el fin de determinar si la aplicación de azufre (S) para el trébol Trifolium repens y el ryegrass Lolium hibridum asociados, a través de su efecto en la fijación de N2 por parte del trébol. Con este propósito se aplicaron cuatro niveles de S (0, 25, 50 y 75 Kg/ha) a suelos de las series Bacatá y Salvio. Se midió el efecto del S sobre el rendimiento, y la acumulación de N por el trébol y el pasto dispuestos solos y asociados, y sobre la fijación de N2 por el trébol. El S aplicado causó aumentos significativos en la producción de materia seca del pasto en el suelo Bacatá y del trébol en el suelo Salvio cuando cada especie se cultivó sola, y además en la concentración o en el contenido de N del trébol y del ryegrass en los diferentes sistemas de cultivo, en el suelo Salvio. En ninguno de los dos suelos sea observaron efectos del S sobre la fijación de N2 por el trébol, lo cual, junto con otras observaciones, indica que los aumentos en materia seca y en N de las plantas se debieron a otras causas que deberían investigarse. Se sugiere estudiar el efecto del S en la mineralización del N en estos suelos

Muon Spin Rotation Measurement of the Magnetic Field Penetration Depth in Ba(Fe0.93 Co0.07)2 As2 : Evidence for Multiple Superconducting Gaps

We have performed transverse field muon spin rotation measurements of single crystals of Ba(Fe$_{0.93}$Co$_{0.07})_2$As$_2$ with the applied magnetic field along the $\hat{c}$ direction. Fourier transforms of the measured spectra reveal an anisotropic lineshape characteristic of an Abrikosov vortex lattice. We have fit the $\mu$SRSR spectra to a microscopic model in terms of the penetration depth $\lambda$ and the Ginzburg-Landau parameter $\kappa$. We find that as a function of temperature, the penetration depth varies more rapidly than in standard weak coupled BCS theory. For this reason we first fit the temperature dependence to a power law where the power varies from 1.6 to 2.2 as the field changes from 200G to 1000G. Due to the surprisingly strong field dependence of the power and the superfluid density we proceeded to fit the temperature dependence to a two gap model, where the size of the two gaps is field independent. From this model, we obtained gaps of $2\Delta_1=3.7k_BT_c$ and $2\Delta_2=1.6k_BT_c$, corresponding to roughly 6 meV and 3 meV respectively

Static magnetic order of Sr4_{4}A2_{2}O6_{6}Fe2_{2}As2_{2} (A = Sc and V) revealed by local probes

Static magnetic order of quasi two-dimensional FeAs compounds Sr4A2O6-xFe2As2, with A = Sc and V, has been detected by 57Fe Moessbauer and muon spin relaxation ({\mu}SR) spectroscopies. The non-superconducting stoichiometric (x = 0) A = Sc system exhibits a static internal/hyperfine magnetic field both at the 57Fe and {\mu}+ sites, indicating antiferromagnetic order of Fe moments below TN = 35 K with ~ 0.1 Bohr magneton per Fe at T = 2 K. The superconducting and oxygen deficient (x = 0.4) A = V system exhibits a static internal field only at the {\mu}+ site below TN ~ 40 K, indicating static magnetic order of V moments co-existing with superconductivity without freezing of Fe moments. These results suggest that the 42622 FeAs systems belong to the same paradigm with the 1111 and 122 FeAs systems with respect to magnetic behavior of Fe moments.Comment: 4 pages 4 figures: for information, contact [email protected]

Superfluid Density and Field-Induced Magnetism in Ba(Fe1-xCox)2As2 and Sr(Fe1-xCox)2As2 Measured with Muon Spin Relaxation

We report muon spin rotation ($\mu$SR) measurements of single crystal Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and Sr(Fe$_{1-x}$Co$_x$)$_2$As$_2$. From measurements of the magnetic field penetration depth $\lambda$ we find that for optimally- and over-doped samples, $1/\lambda(T\to 0)^2$ varies monotonically with the superconducting transition temperature T$_{\rm C}$. Within the superconducting state we observe a positive shift in the muon precession signal, likely indicating that the applied field induces an internal magnetic field. The size of the induced field decreases with increasing doping but is present for all Co concentrations studied.Comment: 7 pages, accepted for publication in Phys. Rev.

The use of Low-Cost Particulate Matter Sensors and Their Future use with Unmanned Aircrafts

Atmospheric pollution is responsible for killing more than seven million people around the globe, according to the World Health Organization. Among the pollutants that contribute to air pollution, aerosols, defined as any liquid or solid particulate matter suspended or dispersed in the atmosphere, are a significant contributor to human morbidity and mortality. Current attempts to measure atmospheric PM are not only cumbersome and costly but also lack high spatiotemporal resolution. Recently, low cost sensors have been used to address these economic, practical, and technological shortcomings. This research aims at using LCSs in diverse environments and across different seasons in order to address the existing infrastructure’s spatial and temporal limitations. Commercial Low-cost sensors will be placed in three different operational modes in order to characterize the horizontal and vertical profiles of atmospheric PM. These modes vary in the dimensions that they sample: (1) stationary 1D collocated with a PM monitor based on the federal equivalent method at a suburban site, (2) mobile on a manned vehicle 2D touring the ERAU campus, and (3) mobile on unmanned vehicle 3D flying at urban, suburban, and rural sites. The different commercial LCSs will be used in this effort, relying on light scattering techniques or optical particle counters. Validation will take place by: (1) collocating LCSs with EPA monitoring stations, (2) comparing data to several other PM measurement devices, and (3) mounting a PM measurement device to a tethered balloon