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Ice cores through an ice sheet can be regarded as a sample of a unique natural deformation experiment lasting up to a million years. Compared to other geological materials forming the earth‘s crust, the microstructure is directly accessible over the full depth. Controlled sublimation etching of polished ice sections reveals pores, air bubbles, grain boundaries and sub-grain boundaries at the surface. The microstructural features emanating at the surface are scanned. A dedicated method of digital image processing has been developed to extract and characterize the grain boundary networks. First preliminary results obtained from an ice core drilled through the Greenland ice sheet are presented. We discuss the role of small grains in grain size analysis and derive from the shape of grain boundaries the acting driving forces for grain boundary migration.

In this paper, we present the development of a multi-channel VHF/UHF ultra-wideband airborne radar sounder and imager for measurements of polar ice sheets. The radar was developed at the Center for Remote Sensing of Ice Sheets (CReSIS) for operation onboard the German Alfred Wegener Institute (AWI) Basler BT-67 aircraft. The system operates from 150 to 600 MHz corresponding to a vertical resolution of 33 cm in free space. The radar is equipped with three 4-m long 8-element antenna subarrays installed under the fuselage and both wings to support 8 transmit and 24 receive channels. The radar waveform from each transmit channel can be configured individually to enable real-time transmit beamforming for wide-swath ice bed imaging of up to 10 km wide. The radar system was deployed to Greenland in the spring of 2016 as a part of the joint AWI/CReSIS test campaign to conduct measurements over glaciers. Sample radar data from this field campaign are presented to illustrate the capability of the radar.

Dark Matter (DM) models providing possible alternative solutions to the small- scale crisis of standard cosmology are nowadays of growing interest. We consider DM interacting with light hidden fermions via well motivated fundamental operators showing the resultant matter power spectrum is suppressed on subgalactic scales within a plausible parameter region. Our basic description of the evolution of cosmological perturbations relies on a fully consistent first principles derivation of a perturbed Fokker-Planck type equation, generalizing existing literature. The cosmological perturbation of the Fokker-Planck equation is presented for the first time in two different gauges, where the results transform into each other according to the rules of gauge transformation. Furthermore, our focus lies on a derivation of a broadly applicable and easily computable collision term showing important phenomenological differences to other existing approximations. As one of the main results and concerning the small-scale crisis, we show the equal importance of vector and scalar boson mediated interactions between DM and light fermions., 27 pages, 5 figures, accepted for publication in JCAP, appendix B added to discuss the impact of higher order terms in the Boltzmann hierarchy

The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier., A range of mechanisms has been proposed for large-scale folding in polar ice sheets. Here, using new three-dimensional reconstructions of such folds in the onset region of the Greenland Petermann Glacier, the authors show that these formed due to flow convergence and the high mechanical anisotropy of ice.

We have developed and validated a quantitative liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI MS/MS) procedure for the simultaneous determination of seven natural and semisynthetic tropane alkaloids in plasma: atropine (d-hyoscyamine/l-hyoscyamine), cocaine, homatropine, ipratropium, littorine, N-butylscopolamine, and scopolamine. Plasma and serum samples were precipitated for deproteinization (recovery 88-94%), followed by reversed-phase-based liquid chromatography prior to positive electrospray ionization for detection by multiple reaction monitoring using a linear ion trap quadrupole mass spectrometer. All analytes were quantified using cocaine-d3 as an internal standard suitable and reliable for robust, precise (coefficient of variation 2-13%), and accurate (87-122%) measurement within a linear range of 3 orders of magnitude (0.05-50 ng/ml plasma). The method was exemplarily applied to stability studies in phosphate-buffered saline, human serum, and rabbit serum. Each alkaloid was incubated separately and samples were taken at distinct incubation time points. Supernatants of diverse alkaloids at corresponding time points were pooled and subjected to simultaneous LC-ESI MS/MS quantification. This combinatorial analysis design allowed us to analyze the stability of samples with a drastically reduced number of chromatographic runs. In the presence of rabbit serum, all tropane alkaloids tested were degraded significantly within minutes to hours, with the exception of the stable semisynthetic compounds ipratropium and N-butylscopolamine. In contrast, in the presence of equal concentrations of human serum, no degradation was observed for any of the compounds, with the exception of cocaine. Relevant enzymes involved in enzymatic degradation are discussed.

Physical review / D 98(11), 115023 (2018). doi:10.1103/PhysRevD.98.115023, Traditional computations of the dark matter (DM) relic abundance, for models where attractive self-interactions are mediated by light force-carriers and bound states exist, rely on the solution of a coupled system of classical on-shell Boltzmann equations. This idealized description misses important thermal effects caused by the tight coupling among force-carriers and other charged relativistic species potentially present during the chemical decoupling process. We develop for the first time a comprehensive ab initio derivation for the description of DM long-range interactions in the presence of a hot and dense plasma background directly from nonequilibrium quantum field theory. Our results clarify a few conceptional aspects of the derivation and show that under certain conditions the finite temperature effects can lead to sizable modifications of DM Sommerfeld-enhanced annihilation and bound-state decay rates. In particular, the scattering and bound states get strongly mixed in the thermal plasma environment, representing a characteristic difference from a pure vacuum theory computation. The main result of this work is a novel differential equation for the DM number density, written down in a form which is manifestly independent under the choice of what one would interpret as a bound or a scattering state at finite temperature. The collision term, unifying the description of annihilation and bound-state decay, turns out to have in general a nonquadratic dependence on the DM number density. This generalizes the form of the conventional Lee-Weinberg equation which is typically adopted to describe the freeze-out process. We prove that our number density equation is consistent with previous literature results under certain limits. In the limit of vanishing finite temperature corrections our central equation is fully compatible with the classical on-shell Boltzmann equation treatment. So far, finite temperature corrected annihilation rates for long-range force systems have been estimated from a method relying on linear response theory. We prove consistency between the latter and our method in the linear regime close to chemical equilibrium., Published by APS, Woodbury, NY

Calculating the abundance of thermally produced dark matter particles has become a standard procedure, with sophisticated methods guaranteeing a precision that matches the percent-level accuracy in the observational determination of the dark matter density. Here, we point out that one of the main assumptions in the commonly adopted formalism, namely local thermal equilibrium during the freeze-out of annihilating dark matter particles, does not have to be satisfied in general. We present two methods for how to deal with such situations, in which the kinetic decoupling of dark matter happens so early that it interferes with the chemical decoupling process: i) an approximate treatment in terms of a coupled system of differential equations for the leading momentum moments of the dark matter distribution, and ii) a full numerical solution of the Boltzmann equation in phase-space. For illustration, we apply these methods to the case of Scalar Singlet dark matter. We explicitly show that even in this simple model the prediction for the dark matter abundance can be affected by up to one order of magnitude compared to the traditional treatment., Comment: 15 pages revtex4 6 figures; corrected missing factor of 4 in scattering rate for scalar singlet example, Eqs. (42,43), as reported in erratum