Observation level combination of SLR and VLBI with c5++: A case study for TIGO

A multi-technique space geodetic analysis software named c5++ has been developed and allows one to combine data on the observation level. With SLR and VLBI modules being ready and tested, this software has been used to compute coordinate time series of the geodetic fundamental station TIGO, located near Concepción, Chile. It can be shown that the combination of space geodetic data on the observation level leads to a significant improvement of station position repeatability, which is an important measure for the stability of a station in the terrestrial reference frame. Moreover, it could be demonstrated that the geophysical signal of the post-seismic tectonic plate movement is usually more complete than detected by any of the two single-technique solutions. In addition, it has been confirmed that so-called nuisance parameters, which are relying on data from a single technique, are not biased when combing observations from different space geodetic techniques.     

Distribution and stable isotopic composition of amino acids from fungal peptaibiotics: assessing the potential for meteoritic contamination

The presence of nonprotein α-dialkyl-amino acids such as α-aminoisobutyric acid (α-AIB) and isovaline (Iva), which are considered to be relatively rare in the terrestrial biosphere, has long been used as an indication of the indigeneity of meteoritic amino acids. However, recent work showing the presence of α-AIB and Iva in peptides produced by a widespread group of filamentous fungi indicates the possibility of a terrestrial biotic source for the α-AIB observed in some meteorites. We measured the amino acid distribution and stable carbon and nitrogen isotopic composition of four α-AIB-containing fungal peptides and compared this data to similar meteoritic measurements. We show that the relatively simple distribution of the C(4) and C(5) amino acids in fungal peptides is distinct from the complex distribution observed in many carbonaceous chondrites. We also identify potentially diagnostic relationships between the stable isotopic compositions of pairs of amino acids from the fungal peptides that may aid in ruling out fungal contamination as a source of meteoritic amino acids.     

Linear Shaped Charge Cutting Property and Charge Cutting Mechanism of Mg-Gd-Y-Zn Alloy

The linear shaped charge cutting technology is an effective technology for aircraft separation. It can separate invalid components from aircrafts timely to achieve light-weight. Magnesium alloy is the lightest metal material, and can be used to cast effective light-weight components of an aircraft construction. However, the application study of the linear shaped charge cutting technology on magnesium alloy components is basically blank. In response to the demand for the linear separation of magnesium alloys, the Mg-12Gd-0.5Y-0.4Zn alloy is selected to carry out the target shaped charge cutting test. The effects of the shaped charge line density, cutting thickness, and mechanical properties on the cutting performance of the alloy are studied. The shaped charge cutting mechanism is analyzed through the notch structure. The results show that the linear shaped charge cutting performance is significantly affected by the penetration and the collapse. The higher the linear density is, the stronger the ability of the linear shaped charge cutter is, and the greater the penetration depth is, which is advantageous. However, the target structure will be damaged when it is too large (e.g., 4.5 g?m-1). Within 12 mm, when the cutting thickness of the target increases, the penetration depth increases. The lower the tensile strength is, the greater the penetration depth is, and the more conducive the penetration depth to the shaped charge cutting is. When the elongation (EL) increases to 12%, the collapse of the target is incomplete and the target cannot be separated. When the tensile strength of the Mg-Gd-Y-Zn alloy is less than 350 MPa, the EL is less than 6.5%, the cutting thickness is less than 12 mm, and the linear shaped charge cutting of the magnesium alloy can be achieved stably.     

Modelling and design of wing tip devices at various flight conditions using a databased aerodynamic prediction tool

A design study of wing tip devices at high and low speeds is described. The basis of the design study is an equivalent drag approach containing both aerodynamic drag gain and structural weight penalty. A comprehensive parameter study is carried out using a rapid aerodynamic prediction tool named Lift and Drag Component Analysis (LIDCA). Adding to an available lifting-line method a databased module for airfoil data is employed that uses results of two-dimensional flow simulations by multidimensional interpolation. Detailed validation studies of the method at high lift and high speed have demonstrated good accuracy. RANS computations of the selected wing tip designs confirm the predicted benefits at cruise condition. The results of the most effective wing tip designs are analysed at both flight conditions. Finally, options for improving the performance at take-off are suggested.     

Locating Current Sheets in the Solar Corona

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection. Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even topological properties of a force-free coronal magnetic field. First, there are separatrices related to magnetic nulls. Through separatrices the magnetic connectivity changes discontinuously. Coronal magnetic nulls are, however, very rare. Second, inspired by the concept of generalized magnetic reconnection without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the magnetic connectivity changes continuously, though strongly. The strength of the connectivity change can be quantified by measuring the squashing of the flux tubes which connect the magnetically conjugated photospheres. We verify the QSL and separatrix concepts by comparing the sites of magnetic nulls and enhanced squashing with the location of current concentrations in the corona. Due to the known difficulties of their direct observation, we simulated coronal current sheets by numerically calculating the response of the corona to energy input from the photosphere, heating a simultaneously observed Extreme Ultraviolet Bright Point. We did not find coronal current sheets at separatrices but at several QSL locations. The reason is that, although the geometrical properties of force-free extrapolated magnetic fields can indeed hint at possible current concentrations, a necessary condition for current sheet formation is the local energy input into the corona.     

Theory and Simulation of Reconnection

Reconnection is a major commonality of solar and magnetospheric physics. It was conjectured by Giovanelli in 1946 to explain particle acceleration in solar flares near magnetic neutral points. Since than it has been broadly applied in space physics including magnetospheric physics. In a special way this is due to Harry Petschek, who in 1994 published his ground breaking solution for a 2D magnetized plasma flow in regions containing singularities of vanishing magnetic field. Petschek’s reconnection theory was questioned in endless disputes and arguments, but his work stimulated the further investigation of this phenomenon like no other. However, there are questions left open. We consider two of them – “anomalous” resistivity in collisionless space plasma and the nature of reconnection in three dimensions. The CLUSTER and SOHO missions address these two aspects of reconnection in a complementary way -- the resistivity problem in situ in the magnetosphere and the 3D aspect by remote sensing of the Sun. We demonstrate that the search for answers to both questions leads beyond the applicability of analytical theories and that appropriate numerical approaches are necessary to investigate the essentially nonlinear and nonlocal processes involved. Necessary are both micro-physical, kinetic Vlasov-equation based methods of investigation as well as large scale (MHD) simulations to obtain the geometry and topology of the acting fields and flows.     

Dust Environment Modelling of Comet 67P/Churyumov-Gerasimenko

Dust is an important constituent of cometary emission; its analysis is one of the major objectives of ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko (C–G). Several instruments aboard Rosetta are dedicated to studying various aspects of dust in the cometary coma, all of which require a certain level of exposure to dust to achieve their goals. At the same time, impacts of dust particles can constitute a hazard to the spacecraft. To conciliate the demands of dust collection instruments and spacecraft safety, it is desirable to assess the dust environment in the coma even before the arrival of Rosetta. We describe the present status of modelling the dust coma of 67P/C–G and predict the speed and flux of dust in the coma, the dust fluence on a spacecraft along sample trajectories, and the radiation environment in the coma. The model will need to be refined when more details of the coma are revealed by observations. An overview of astronomical observations of 67P/C–G is given, because model parameters are derived from this data if possible. For quantities not yet measured for 67P/C–G, we use values obtained for other comets, e.g. concerning the optical and compositional properties of the dust grains. One of the most important and most controversial parameters is the dust mass distribution. We summarise the mass distribution functions derived from the in-situ measurements at comet 1P/Halley in 1986. For 67P/C–G, constraining the mass distribution is currently only possible by the analysis of astronomical images. We find that both the dust mass distribution and the time dependence of the dust production rate of 67P/C–G are those of a fairly typical comet.     

Size and cell number of the utricle in kinetotically swimming fish: a parabolic aircraft flight study.

Humans taking part in parabolic aircraft flights (PAFs) may suffer from space motion sickness (SMS, a kinetosis). Since it has been repeatedly shown earlier that some fish of a given batch also reveal a kinetotic behavior during PAFs (especially so-called spinning movements and looping responses) and due to the homology of the vestibular apparatus among all vertebrates, fish can be used as model systems to investigate the origin of susceptibility to motion sickness. Therefore, we examined the utricular maculae (they are responsible for the internalization of gravity in teleosteans) of fish swimming kinetotically at microgravity in comparison with animals from the same batch who swam normally. On the histological level, it was found that the total number of both sensory and supporting cells of the utricular maculae did not differ between kinetotic animals as compared to normally swimming fish. Cell density (sensory and supporting cells/100 micrometers2), however, was reduced in kinetotic animals (p<0.0001), which seemed to be due to malformed epithelial cells (increase in cell size) of the kinetotic specimens. Susceptibility to kinetoses may therefore originate in malformed sensory epithelia.