3D Hydrophobic Moment Vectors as a Tool to Characterize the Surface Polarity of Amphiphilic Peptides

AbstractThe interaction of membranes with peptides and proteins is largely determined by their amphiphilic character. Hydrophobic moments of helical segments are commonly derived from their two-dimensional helical wheel projections, and the same is true for β-sheets. However, to the best of our knowledge, there exists no method to describe structures in three dimensions or molecules with irregular shape. Here, we define the hydrophobic moment of a molecule as a vector in three dimensions by evaluating the surface distribution of all hydrophilic and lipophilic regions over any given shape. The electrostatic potential on the molecular surface is calculated based on the atomic point charges. The resulting hydrophobic moment vector is specific for the instantaneous conformation, and it takes into account all structural characteristics of the molecule, e.g., partial unfolding, bending, and side-chain torsion angles. Extended all-atom molecular dynamics simulations are then used to calculate the equilibrium hydrophobic moments for two antimicrobial peptides, gramicidin S and PGLa, under different conditions. We show that their effective hydrophobic moment vectors reflect the distribution of polar and nonpolar patches on the molecular surface and the calculated electrostatic surface potential. A comparison of simulations in solution and in lipid membranes shows how the peptides undergo internal conformational rearrangement upon binding to the bilayer surface. A good correlation with solid-state NMR data indicates that the hydrophobic moment vector can be used to predict the membrane binding geometry of peptides. This method is available as a web application on http://www.ibg.kit.edu/HM/

In-Orbit SAR Performance of TerraSAR-X

TerraSAR-X is the first German Radar satellite for scientific and commercial applications. The project is a public-private partnership between DLR and EADS Astrium GmbH. TerraSAR-X consists of a high resolution Synthetic Aperture Radar at X-Band. The radar antenna is based on active phased array technology that allows the control of many different instrument parameters and operational modes (Stripmap, ScanSAR and Spotlight) with various polarizations. Following the TerraSAR-X launch, scheduled for February 2007, it is planned a six month Commissioning Phase covering the characterization and verification of the SAR mission. Within this phase, the Overall SAR System Performance (OSSP) takes care of the correct working and interaction of all SAR system elements essential for obtaining an optimum SAR Performance. The paper covers the first in-orbit characterization and verification results of the SAR system performance for TerraSAR-X operational and experimental modes. This characterization is divided into four phases: Initial Characterization, Scene Characterization –both mostly based on basic and experimental products-, and Verification of TS-X Instrument Command Generation. The different optimization strategies and performance trade-offs are discussed and presented in the paper, including very first TerraSAR-X images. The result of the real SAR data analysis determines the final system baseline and thus the final image quality, e.g. Temperature compensation, Total Zero Doppler Steering, Up/down chirp toggling, transmitted bandwidth, timing interferences, etc. The first section of the paper introduces the activities carried out during the Commissioning Phase for the TerraSAR-X SAR system performance characterization/verification. In the second section, the strategies for the performance optimization and characterization are presented. Finally, the in-orbit SAR performance results are given in section three

Bistatic Experiment Using TerraSAR-X and DLR’s new F-SAR System

A bistatic X-band experiment was successfully performed early November 2007. TerraSAR-X was used as transmitter and DLR’s new airborne radar system F-SAR, which was programmed to acquire data in a quasi-continuous mode to avoid echo window synchronization issues, was used as bistatic receiver. Precise phase and time referencing between both systems, which is essential for obtaining high resolution SAR images, was derived during the bistatic processing. Hardware setup and performance analyses of the bistatic configuration are pre-sented together with first processing results that verify the predicted synchronization and imaging performance

Stuck Bit Error Identification for the TerraSAR-X and TanDEM-X Onboard Memory

Errors in memory storage devices in the form of erroneous bits induced by radiation are a common issue for every space- craft in orbit. Therefore, well established techniques detect and directly correct these errors in the storage hardware. Sporadically single memory cells can temporarily get “stuck” at a false bit in which case they cannot be corrected. Those stuck bits can persist up to several months generating the same errors during every memory scrubbing cycle. In order to assess the current memory status a method to distinguish between regular and stuck-bit errors is needed. This paper therefore presents a classification approach based on the DBSCAN method where stuck bits are identified as outliers and clustered accordingly. The approach first is verified with simulated data that resembles the error structure of memory errors on TerraSAR-X and TanDEM-X. Subsequently, the method is validated with the memory errors recorded by both satellites throughout their lifetime

Experimental Demonstration of Nadir Echo Removal in SAR Using Waveform Diversity and Dual-Focus Postprocessing

Synthetic aperture radar (SAR) provides high-resolution images for remote sensing applications regardless of sunlight and weather conditions. The pulsed operation of SAR may lead to an occurrence of nadir echoes in SAR images that significantly affect the image quality in case the pulse repetition frequency (PRF) is not properly constrained within the SAR system design. As an alternative, pulse-to-pulse variation of the transmitted waveform and dual-focus postprocessing can be exploited to remove the nadir echo and alleviate the PRF constraints (also in ScanSAR operation). This work provides a demonstration of the latter concept through an experimental acquisition of the TerraSAR-X satellite. The experiment is designed by selecting the scene and the acquisition parameters in order to have the nadir echo appearing in the SAR image. The waveform variation is achieved by alternating up- and down-chirps on transmit. The analysis of the results shows the effectiveness of dual-focus postprocessing for nadir echo suppression

Concurrent Imaging for TerraSAR-X: Wide-Area Imaging paired with High-Resolution Capabilities

The concurrent imaging technique enables parallel acquisitions with different beams or modes, e.g., a wide area Stripmap mode with a high resolution Spotlight mode. Such a concurrent Stripmap/Spotlight imaging technique is investigated for TerraSAR-X. This technique employs a pulse-topulse interleaving scheme to acquire two acquisitions - even of disjunctive areas - at the same time, offering products with different resolution and coverage portfolios. This capability is especially interesting for customers interested in an overview of a larger area but at the same time observing an area of interest with higher resolution, e.g., for infrastructure monitoring or reconnaissance applications. The basic concept, as well as the driving system parameters, are discussed in detail, together with a coverage analysis revealing the high availability rate of the mode combinations on a global scale. A processing approach reusing a substantial part of the existing infrastructure is described and exemplary acquisitions are shown, together with a detailed performance analysis with respect to resolution and ambiguities

TerraSAR-X Ultra Stable Oscillator Temperature Drift Compensation

After 15 years of successful radar operations in space, the German SAR satellite TerraSAR-X (TSX) showed peculiarities in the frequency of the Ultra Stable Oscillator (USO) since 1st of Nov. 2022 13:56 UTC. In conclusion, we will show at the workshop how we can maintain the excellent performance of TSX despite the new challenges the ageing instrument poses

DELTA-K WIDEBAND SAR INTERFEROMETRY FOR DEM GENERATION AND PERSISTENT SCATTERERS USING TERRASAR-X

ABSTRACT Wideband SAR systems such as TerraSAR-X allow estimation of the absolute interferometric phase without resorting to error prone phase unwrapping. This is achieved through the delta-k technique that exploits frequency diversity within the range bandwidth to simulate a SAR system with a much longer carrier wavelength. This benefits all interferometric applications including DEM generation and land surface motion determination. Here we present the results of an ESA study (21318/07/NL/HE) into using delta-k absolute phase estimation for DEM generation and PSI (Persistent Scatterer Interferometry). Using TerraSAR-X data, examples from a delta-k DEM generation system are shown which avoid the errors induced by conventional phase unwrapping. For PSI, the possibilities of absolute phase estimation for a single PS are explored in theory and examples where wideband estimation is compared to conventional PSI processing for a stack of acquisitions over Paris

Autonomic and peripheral nervous system function in acute tick-borne encephalitis

ObjectivesTick-borne encephalitis (TBE) is an emerging flaviviral zoonosis in Central and Eastern Europe. TBE can present as meningitis, meningoencephalitis, or meningoencephalomyelitis. Dysfunction of the autonomic (ANS) and peripheral motoric and sensory nervous system (PNS) might contribute to acute and long-term complications. We aimed to examine, whether the ANS and PNS are affected in acute TBE. MethodsFourteen patients with acute TBE, 17 with diabetic polyneuropathy (d-PNP), and 30 healthy controls (HC) were examined in our single-center, prospective study. ANS and PNS function was assessed by time- and frequency-domain parameters of the heart rate (HR) variability at rest and deep respiration, and by sural and tibial nerve neurography. Primary endpoint was the HR variability at rest measured by root mean square of the successive differences (RMSSD). Autonomic symptoms and quality of life (QoL) were assessed by questionnaires. ResultsTick-borne encephalitis patients had a lower RMSSD at rest (TBE 13.17.0, HC 72.7 +/- 48.3; P<0.001) and deep respiration (TBE 42.8 +/- 27.0, HC 109.7 +/- 68.8; P<0.01), an increased low-frequency to high-frequency power component ratio at rest (TBE 4.0 +/- 4.0, HC 0.8 +/- 0.5; P<0.001), and a higher minimal heart rate at rest (TBE 85.4 +/- 7.0, HC 69.5 +/- 8.5; P<0.001), all similar to patients with d-PNP, indicating sympathovagal imbalance with increased sympathetic activation. Compared to HC, sural and tibial nerve conduction velocities and action potential amplitudes were reduced, ANS symptoms were more frequent, and QoL was lower in patients with TBE. ConclusionsThe ANS and to a lesser degree the PNS are affected by acute TBE, which could potentially contribute to short- and long-term morbidity