Strength design model for thin-walled structures

In this paper, the finite element analysis of the stress-strain state for cylindrical structures is discussed. In this case, various fundamental hypotheses can be used in the framework of a model that is of interest for design and optimization. Numerical examples are presented to evaluate the possibilities of this model.     

The Magnetospheric Multiscale Magnetometers

The success of the Magnetospheric Multiscale mission depends on the accurate measurement of the magnetic field on all four spacecraft. To ensure this success, two independently designed and built fluxgate magnetometers were developed, avoiding single-point failures. The magnetometers were dubbed the digital fluxgate (DFG), which uses an ASIC implementation and was supplied by the Space Research Institute of the Austrian Academy of Sciences and the analogue magnetometer (AFG) with a more traditional circuit board design supplied by the University of California, Los Angeles. A stringent magnetic cleanliness program was executed under the supervision of the Johns Hopkins University’s Applied Physics Laboratory. To achieve mission objectives, the calibration determined on the ground will be refined in space to ensure all eight magnetometers are precisely inter-calibrated. Near real-time data plays a key role in the transmission of high-resolution observations stored on board so rapid processing of the low-resolution data is required. This article describes these instruments, the magnetic cleanliness program, and the instrument pre-launch calibrations, the planned in-flight calibration program, and the information flow that provides the data on the rapid time scale needed for mission success.     

The Magnetic Field Pile-up and Density Depletion in the Martian Magnetosheath: A Comparison with the Plasma Depletion Layer Upstream of the Earth's Magnetopause

Using magnetometer and electron observations from the Mars Global Surveyor (MGS) and the Wind spacecraft we show that the region of magnetic field pile-up and density decrease located between the Martian ionosphere and bow shock exhibit strong similarities with the plasma depletion layer (PDL) observed upstream of the Earth's magnetopause in the absence of magnetic reconnection when the magnetopause is a solid obstacle in the solar wind. A PDL is formed upstream of the terrestrial magnetopause when the magnetic field piles up against the obstacle and particles in the pile-up region are squeezed away from the high magnetic pressure region along the field lines as the flux tubes convect toward the magnetopause. We here discuss the possibility that at least part of the region of magnetic field pile-up and density depletion upstream of Mars may be formed by the same physical processes which generate the PDL upstream of the Earth's magnetopause. More complete ion, electron, and neutral measurements are needed to conclusively determine the relative importance of the plasma depletion process versus exospheric processes.     

Early morning enhancement in ionospheric electron density during intense magnetic storms

This study reports on ionospheric disturbances that occurred in the early morning hours in the South American–Atlantic sector during a few intense/super storm events. The events were observed at latitudes close to the southern crest of the equatorial ionization anomaly (EIA) as an unusual intensification of the F region electron density peak at local times when the EIA is not usually developed. All the events were observed at pre dawn-morning hours, under conditions of northward interplanetary geomagnetic field. Large scale traveling ionospheric disturbances that are launched during highly disturbed conditions and/or equatorward surges in the thermospheric meridional winds seem to be the most probable causes of the observed disturbances.     

Kink-like mode of a double gradient instability in a compressible plasma current sheet

A linear MHD instability of the electric current sheet, characterized by a small normal magnetic field component, varying along the sheet, is investigated. The tangential magnetic field component is modeled by a hyperbolic function, describing Harris-like variations of the field across the sheet. For this problem, which is formulated in a 3D domain, the conventional compressible ideal MHD equations are applied. By assuming Fourier harmonics along the electric current, the linearized 3D equations are reduced to 2D ones. A finite difference numerical scheme is applied to examine the time evolution of small initial perturbations of the plasma parameters. This work is an extended numerical study of the so called “double gradient instability”, – a possible candidate for the explanation of flapping oscillations in the magnetotail current sheet, which has been analyzed previously in the framework of a simplified analytical approach for an incompressible plasma. The dispersion curve is obtained for the kink-like mode of the instability. It is shown that this curve demonstrates a quantitative agreement with the previous analytical result. The development of the instability is investigated also for various enhanced values of the normal magnetic field component. It is found that the characteristic values of the growth rate of the instability shows a linear dependence on the square root of the parameter, which scales uniformly the normal component of the magnetic field in the current sheet.     

New results on spin determination of nanosatellite BLITS from High Repetition Rate SLR data

The nanosatellite BLITS (Ball Lens In The Space) demonstrates a successful design of the new spherical lens type satellite for Satellite Laser Ranging (SLR). The spin parameters of the satellite were calculated from more than 1000 days of SLR data collected from 6 High Repetition Rate (HRR) systems: Beijing, Changchun, Graz, Herstmonceux, Potsdam, Shanghai.     

E region electric fields at the dip equator and anomalous conductivity effects

Zonal and vertical electric fields were estimated at E region heights in the Brazilian sector. Zonal electric fields are obtained from the vertical electric fields based on their relation through the Hall-to-Pedersen ionospheric conductivities ratio. The technique for obtaining the vertical electric field is based on its proportionality to the Doppler velocities of type 2 irregularities as detected by coherent radars. The 50 MHz backscatter coherent (RESCO) radar was used to estimate the Doppler velocities of the type 2 irregularities embedded in the equatorial electrojet. A magnetic field-line integrated conductivity model was developed to provide the conductivities. It considers a multi-species ionosphere and a multi-species neutral atmosphere, and uses the IRI 2007, the MISIS 2000 and the IGRF 10 models as input parameters for ionosphere, neutral atmosphere and Earth’s magnetic field, respectively. The ion-neutral collision frequencies of all the species are combined through the momentum transfer collision frequency equation, and different percentages of electron-neutral collisions were artificially included for studying the implication of such increase in the zonal electric field, which resulted ranging from 0.13 to 0.49 mV/m between the 8 and 18 h (LT), under quiet magnetic conditions.     

Taxonomy of Human Wayfinding Tasks: A Knowledge-Based Approach

Abstract

Although the term “Wayfinding” has been defined by several authors, it subsumes a whole set of tasks that involve different cognitive processes, drawing on different cognitive components. Research on wayfinding has been conducted with different paradigms using a variety of wayfinding tasks. This makes it difficult to compare the results and implications of many studies. A systematic classification is needed in order to determine and investigate the cognitive processes and structural components of how humans solve wayfinding problems. Current classifications of wayfinding distinguish tasks on a rather coarse level or do not take the navigator's knowledge, a key factor in wayfinding, into account. We present an extended taxonomy of wayfinding that distinguishes tasks by external constraints as well as by the level of spatial knowledge that is available to the navigator. The taxonomy will help to decrease ambiguity of wayfinding tasks and it will facilitate understanding of the differentiated demands a navigator faces when solving wayfinding problems.     

Modeling Particle Fluxes and Absorbed Dose for Protection from Cosmic Rays Using the SHIELD Transport Code

Cosmic Research - A special version of the SHIELD transport code has been developed intended for radiation protection purposes in space. The calculation of the fluxes of primary and secondary...