Gradient Index Metamaterial Based on Slot Elements

We present a gradient-index (GRIN) metamaterial based on an array of annular slots. The structure allows a large variation of the effective refractive index under normal-to-plane incidence and thus enables the construction of GRIN devices consisting of only a small number of functional layers. Using full-wave simulations, we demonstrate the annular slot concept by means of a 3-unit-cell thin GRIN lens for the terahertz (THz) range. In the presented realizations, we achieved an index contrast of Delta n = 1.5 resulting in a highly refractive lens suitable for focusing THz radiation to a spot size smaller than the wavelength.Comment: 4 pages, 5 figure

Airborne lidar observations supporting the ADM-Aeolus mission for global wind profiling

The Atmospheric Dynamics Mission ADM-Aeolus of ESA will be the first lidar mission to sense the global wind field from space. The instrument is based on a direct-detection Doppler lidar operating at 354.9 nm with two spectrometers for aerosol/cloud and molecular backscatter. In order to assess the performance of the Doppler lidar ALADIN on ADM-Aeolus and to optimize the retrieval algorithms with atmospheric signals, an airborne prototype – the ALADIN Airborne Demonstrator A2D – was developed. The A2D was the first airborne direct-detection Doppler lidar with its maiden flight on the DLR Falcon aircraft in 2005. Three airborne campaigns with a coherent-detection 2-μm wind lidar and the direct-detection wind lidar A2D were performed for pre-launch validation of Aeolus from 2007-2009. Furthermore, a unique experiment for resolving the Rayleigh-Brillouin spectral line shape in the atmosphere was accomplished in 2009 with the A2D from a mountain observatory at an altitude of 2650 m. Results of this experiment and the latest airborne campaign in the vicinity of Greenland and Iceland will be discussed

In-Plane Focusing of Terahertz Surface Waves on a Gradient Index Metamaterial Film

We designed and implemented a gradient index metasurface for the in-plane focusing of confined terahertz surface waves. We measured the spatial propagation of the surface waves by two-dimensional mapping of the complex electric field using a terahertz near-field spectroscope. The surface waves were focused to a diameter of 500 \micro m after a focal length of approx. 2 mm. In the focus, we measured a field amplitude enhancement of a factor of 3.Comment: 6 pages, 4 figure

Airborne Coherent Doppler Wind Lidar measurements of vertical and horizontal wind speeds for the investigation of gravity waves

Gravity waves are well known phenomena in the atmosphere, but there is still a lack of knowledge of their life cycle including excitation, propagation and dissipation mechanisms. In order to investigate these topics, DLR’s coherent Doppler wind lidar system was recently deployed during 3 airborne campaigns on the Falcon F20 research aircraft, namely the GW-LCYCLE I campaign (Kiruna, Sweden, December 2013), the DEEPWAVE campaign (Christchurch, New Zealand, June/July 2014) and the GW-LCYCLE II campaign (Kiruna, Sweden, January/February 2016). In this paper, a case study based on a research flight performed during GW-LCYCLE I is discussed and a method for correcting horizontal wind contribution in the vertical wind retrieval based on ECMWF data is introduced. The remaining systematic error of the retrieved vertical wind is estimated to be less than 10 cm/s. A measurement of a flight leg across the Scandinavian mountain ridge is used to characterize gravity waves during strong forcing conditions. The measured vertical wind reaches amplitudes of larger than ± 3 m/s and horizontal wavelengths of 10 km to 20 km. A comparison with WRF-model calculations shows a quite good representation of the horizontal structure of the vertical wind. The amplitude however is obviously underestimated by a factor of 2 and shows maximum wind speeds of ± 1.5 m/s

Metamaterial near-field sensor for deep-subwavelength thickness measurements and sensitive refractometry in the terahertz frequency range

We present a metamaterial-based terahertz (THz) sensor for thickness measurements of subwavelength-thin materials and refractometry of liquids and liquid mixtures. The sensor operates in reflection geometry and exploits the frequency shift of a sharp Fano resonance minimum in the presence of dielectric materials. We obtained a minimum thickness resolution of 12.5 nm (1/16000 times the wavelength of the THz radiation) and a refractive index sensitivity of 0.43 THz per refractive index unit. We support the experimental results by an analytical model that describes the dependence of the resonance frequency on the sample material thickness and the refractive index.Comment: 10 pages, 5 figure

ADM-Aeolus pre-launch activities and recent advances in spaceborne and airborne Wind Lidar Systems

The first space-borne wind lidar mission ADM-Aeolus from ESA is currently scheduled for launch by mid-2017. For the preparation of the Aeolus validation, an airborne field experiment was performed during 3 weeks in May 2015 with the DLR Falcon and the NASA DC-8 aircraft. For the first time 4 wind lidars were deployed during an airborne campaign including two coherent and two direct-detection wind lidars at a wavelength of 2μm and 355 nm. A total of 7 coordinated flights of the Falcon and DC-8 yielded an extensive dataset. Additionally, DLR’s airborne coherent Doppler Wind Lidar was recently deployed in 3 coordinated airborne campaigns aiming to investigate the life cycle of gravity waves from ground up to the mesosphere. The horizontal and vertical wind measurements of the lidar provide valuable data for characterizing tropospheric gravity waves and background wind conditions

Molecular dissection of Wnt3a-Frizzled8 interaction reveals essential and modulatory determinants of Wnt signaling activity

Background: Wnt proteins are a family of secreted signaling molecules that regulate key developmental processes in metazoans. The molecular basis of Wnt binding to Frizzled and LRP5/6 co-receptors has long been unknown due to the lack of structural data on Wnt ligands. Only recently, the crystal structure of the Wnt8-Frizzled8-cysteine-rich-domain (CRD) complex was solved, but the significance of interaction sites that influence Wnt signaling has not been assessed. Results: Here, we present an extensive structure-function analysis of mouse Wnt3a in vitro and in vivo. We provide evidence for the essential role of serine 209, glycine 210 (site 1) and tryptophan 333 (site 2) in Fz binding. Importantly, we discovered that valine 337 in the site 2 binding loop is critical for signaling without contributing to binding. Mutations in the presumptive second CRD binding site (site 3) partly abolished Wnt binding. Intriguingly, most site 3 mutations increased Wnt signaling, probably by inhibiting Wnt-CRD oligomerization. In accordance, increasing amounts of soluble Frizzled8-CRD protein modulated Wnt3a signaling in a biphasic manner. Conclusions: We propose a concentration-dependent switch in Wnt-CRD complex formation from an inactive aggregation state to an activated high mobility state as a possible modulatory mechanism in Wnt signaling gradients

Airborne coherent wind lidar measurements of the momentum flux profile from orographically induced gravity waves

In the course of the GW-LCYCLE II campaign, conducted in Jan/Feb 2016 from Kiruna, Sweden, coherent Doppler wind lidar (2 µm DWL) measurements were performed from the DLR Falcon aircraft to investigate gravity waves induced by flow across the Scandinavian Alps. During a mountain wave event on 28 January 2016, a novel momentum flux (MF) scan pattern with fore and aft propagating laser beams was applied to the 2 µm DWL. This allows us to measure the vertical wind and the horizontal wind along the flight track simultaneously with a high horizontal resolution of ≈800 m and hence enables us to derive the horizontal MF profile for a broad wavelength spectrum from a few hundred meters to several hundred kilometers. The functionality of this method and the corresponding retrieval algorithm is validated using a comparison against in situ wind data measured by the High Altitude and Long Range (HALO) aircraft which was also deployed in Kiruna for the POLSTRACC (Polar Stratosphere in a Changing Climate) campaign. Based on that, the systematic and random error of the wind speeds retrieved from the 2 µm DWL observations are determined. Further, the measurements performed on that day are used to reveal significant changes in the horizontal wavelengths of the vertical wind speed and of the leg-averaged momentum fluxes in the tropopause inversion layer (TIL) region, which are likely to be induced by interfacial waves as recently presented by Gisinger et al. (2020).</p

Feasibility of FPGA-based Computations of Transition Densities in Quantum Many-Body Systems

This thesis presents the results from a feasibility study of implementing calculations of transition densities for quantum many-body systems on FPGA hardware. Transition densities are of interest in the field of nuclear physics as a tool when calculating expectation values for different operators. Specifically, this report focuses on transition densities for bound states of neutrons. A computational approach is studied, in which FPGAs are used to identify valid connections for one-body operators. Other computational steps are performed on a CPU. Three different algorithms that find connections are presented. These are implemented on an FPGA and evaluated with respect to hardware cost and performance. The performance is also compared to that of an existing CPU-based code, Trdens. The FPGA used to implement the proposed designs was a Xilinx Virtex 6, built into Maxeler’s MAX3 card. It was concluded that the FPGA was able to find the connections of a one-body operator in a fraction of the time used by Trdens, ran on a single CPUcore. However, the CPU-based conversion of the connections to the form in which Trdens presents them, was much more time-consuming. For FPGAs to be feasible, it is hence necessary to accelerate the CPU-based computations or include them into the FPGA-implementations. Therefore, we recommend further investigations regarding calculations of the final representation of transition densities on FPGAs, without the use of an off-FPGA computation