Observations of Comet 9P/Tempel 1 around the Deep Impact event by the OSIRIS cameras onboard Rosetta

The OSIRIS cameras on the Rosetta spacecraft observed Comet 9P/Tempel 1 from 5 days before to 10 days after it was hit by the Deep Impact projectile. The Narrow Angle Camera (NAC) monitored the cometary dust in 5 different filters. The Wide Angle Camera (WAC) observed through filters sensitive to emissions from OH, CN, Na, and OI together with the associated continuum. Before and after the impact the comet showed regular variations in intensity. The period of the brightness changes is consistent with the rotation period of Tempel 1. The overall brightness of Tempel 1 decreased by about 10% during the OSIRIS observations. The analysis of the impact ejecta shows that no new permanent coma structures were created by the impact. Most of the material moved with . Much of it left the comet in the form of icy grains which sublimated and fragmented within the first hour after the impact. The light curve of the comet after the impact and the amount of material leaving the comet ( of water ice and a presumably larger amount of dust) suggest that the impact ejecta were quickly accelerated by collisions with gas molecules. Therefore, the motion of the bulk of the ejecta cannot be described by ballistic trajectories, and the validity of determinations of the density and tensile strength of the nucleus of Tempel 1 with models using ballistic ejection of particles is uncertain.     

Testing fundamental physics with distant star clusters: theoretical models for pressure-supported stellar systems

We investigate the mean velocity dispersion and the velocity dispersion profile of stellar systems in modified Newtonian dynamics (MOND), using the N -body code n-mody , which is a particle-mesh-based code with a numerical MOND potential solver developed by Ciotti, Londrillo & Nipoti. We have calculated mean velocity dispersions for stellar systems following Plummer density distributions with masses in the range of 10⁴ to  10⁹ M_⊙  and which are either isolated or immersed in an external field. Our integrations reproduce previous analytic estimates for stellar velocities in systems in the deep MOND regime  ( a _i, a _e≪ a ₀)  , where the motion of stars is either dominated by internal accelerations  ( a _i≫ a _e)  or constant external accelerations  ( a _e≫ a _i)  . In addition, we derive for the first time analytic formulae for the line-of-sight velocity dispersion in the intermediate regime  ( a _i∼ a _e∼ a ₀)  . This allows for a much-improved comparison of MOND with observed velocity dispersions of stellar systems. We finally derive the velocity dispersion of the globular cluster Pal 14 as one of the outer Milky Way halo globular clusters that have recently been proposed as a differentiator between Newtonian and MONDian dynamics.     

Predicting metal detector performance for landmine clearance: soil magnetic map of Angola

A map depicting predicted classes of soil magnetic susceptibility in Angola was produced. The map is based on a classification system for the susceptibility of tropical soils set up by the authors and a 1:2,000,000 scale FAO soil map. Statistical data of two large groups of parent rock—ultrabasic, basic and intermediate igneous rocks on the one hand and acid igneous rocks and some slightly metamorphosed rocks and clastic sediments on the other—had been linked to three associated degrees of weathering. These determining factors were used to classify Angolan soils, and the overall method is semi-quantitative. The resulting map shows that easily available pedological information as given by FAO soil maps is generally appropriate to predict soil magnetic susceptibility. Potential metal detector performance failures may be predicted. The resulting information is a useful tool for planning the use of appropriate techniques in landmine clearance operations.     

On the current profile in the German Bight: A two-month BroadBand ADCP time series of high vertical resolution

Summary A bottom mounted BroadBand ADCP was deployed for about two months in the German Bight (54° 15.3′, N, 7° 35.5′ E) at 40 m depth. The ADCP recorded current data and echo intensity between 3 and 38m depth with a vertical resolution of 1 m. The data, which provide continuous vertical current profiles, are investigated with regard to the vertical variations of residual and tidal currents and kinetic energies. To investigate the temporal variability of the current profiles, the time series are subdivided into 8-day intervals. Furthermore, the data are compared with historical data. According to the ADCP profiles, the water column can be subdivided into three layers: A primarily wind-driven near-surface layer (∼10m), a middepth layer with great directional variability, and a near-bottom layer of about 10 m thickness with a strictly logarithmic current profile.

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über das Stromprofil in der Deutschen Bucht: Eine zweimonatige BroadBand ADCP Zeitserie mit hoher vertikaler Aufl?sung

Zusammenfassung Ein am Boden stehender BroadBand ADCP wurde für zwei Monate in der Deutschen Bucht (54° 15.3′ N, 7° 35.5′ E) in 40 m Wassertiefe eingesetzt. Er registrierte Str?mungsdaten und Echointensit?t zwischen 3 und 38 m Wassertiefe mit einer vertikalen Aufl?sung von 1 m. Dieser Datensatz, der kontinuierliche vertikale Stromprofile liefert, wird hinsichtlich der vertikalen Variation von Rest- und Gezeitenstr?men und kinetischer Energie analysiert. Zur Untersuchung der zeitlichen Variabilit?t der Stromprofile wird die Gesamtzeitserie in 8-Tage-Intervalle unterteilt. Ferner werden die Ergebnisse mit historischen Messungen verglichen. Aus den ADCP-Profilen ergibt sich eine prinzipielle Dreiteilung der Wassers?ule: Eine vorwiegend windgetriebene oberfl?chennahe Schicht (∼10m), eine mittlere Schicht mit hoher Richtungsvariabilit?t und eine etwa 10 m m?chtige Bodenschicht mit streng logarithmischem Stromprofil.

     

Characterization of sediments in an abandoned mining area; a case study of Mansfeld region,Germany

The distribution of selected heavy metals, including some radionuclides, metalloids and non-metals was determined in stream sediments in a region influenced by abandoned copper mining and ore processing activities. A considerable amount of the ore processing waste with a very complex composition and highly elevated concentrations of zinc, sulfur, lead, copper, arsenic, and a lot of other elements in the range between 100 and 1,000 mg/kg (Sb, Mn, Ni, Cr, Cd, Hg, and Ag) was piled up on mine dumps. The dispersion of the pollutants originating from this source and their environmental impact were investigated. Both, sediments and original waste material were studied to indicate the pathways and the mobilization behavior of different pollutants. For this purpose, the process of the elution of pollutants by application of different fractionation schemes was studied. The capabilities of different analytical techniques are shown for the analysis of solid samples (X-ray fluorescence spectrometry, Gamma-spectrometry) and liquid ones (ICP-atomic emission spectrometry, ICP-mass spectrometry and different techniques of atomic absorption). Additionally, the coupling of ion chromatography and ICP-MS detection was used to study the distribution of arsenic species in the sediment cores of a lake which acts as a natural sink for the region.     

The Mesozoic–Cenozoic structural framework of the Bay of Kiel area, western Baltic Sea

A dense grid of multichannel high-resolution seismic sections from the Bay of Kiel in the western Baltic Sea has been interpreted in order to reveal the Mesozoic and Cenozoic geological evolution of the northern part of the North German Basin. The overall geological evolution of the study area can be separated into four distinct periods. During the Triassic and the Early Jurassic, E–W extension and the deposition of clastic sediments initiated the movement of the underlying Zechstein evaporites. The deposition ceased during the Middle Jurassic, when the entire area was uplifted as a result of the Mid North Sea Doming. The uplift resulted in a pronounced erosion of Upper Triassic and Lower Jurassic strata. This event is marked by a clear angular unconformity on all the seismic sections. The region remained an area of non-deposition until the end of the Early Cretaceous, when the sedimentation resumed in the area. Throughout the Late Cretaceous the sedimentation took place under tectonic quiescence. Reactivated salt movement is observed at the Cretaceous Cenozoic transition as a result of the change from an extensional to compressional regional stress field. The vertical salt movement influenced the Cenozoic sedimentation and resulted in thin-skinned faulting.     

Arsenic fixation on iron-hydroxide-rich and plant litter-containing sediments in natural environments

Iron-hydroxide-rich and plant litter-containing sediments from natural sites contaminated with uranium mine tailing leachates were examined for their ability to adsorb arsenic. The samples with high contents of iron hydroxides (Fe_total concentration, >300 g kg⁻¹) exhibited remarkable fixation of arsenic (up to 40 g As kg⁻¹). This value corresponded approximately to the supersaturation point for natural iron hydroxides under the present conditions, and it was significantly lower than the value found for synthetic iron hydroxides. There was a strong correlation (R=0.8999) between the concentration of iron and that of arsenic at low arsenic contents, indicating adsorption on strong binding sites. Although all the samples had noticeable contents of organic carbon (plant litter), calcium, and manganese, no obvious effect of these elements on arsenic fixation could be detected. The amount of iron hydroxides was found the only fixation-controlling parameter immediately below a leaching water source.     

High coronal structure of high velocity solar wind stream sources

When solar wind plasma in the trailing (eastern) edge of a high-speed stream is mapped back to its estimated source in the high corona using the constant radial velocity (EQRH) approximation, a large range of velocities appears to come from a restricted range in longitude, often only a few degrees. This actually constitutes a sharp eastern coronal boundary for the solar wind stream source, and demands that the boundary have a three-dimensional structure. Using interplanetary data, we infer a systematic variation in source altitude (identified approximately with the Alfvén point), with faster solar wind attaining its interplanetary characteristics at lower altitudes. This also affects the accuracy of the source longitude estimates, so that we infer a width in the high corona of 4–6° for the source of the trailing edges of streams which appear to originate from a single longitude. We demonstrate that the possible systematic interplanetary effects (in at least some cases) are not large ( 2° in heliocentric longitude). The relatively sharp boundaries imply that high-speed streams are well-defined structures all the way down to their low coronal sources, and that the magnetic field structure controls the propagation of the plasma through the corona out to the vicinity of the Alfvén point ( 20 R ).     

Association of X-ray arches with chromospheric neutral lines

Daily maps of magnetic neutral lines derived from H observations have been superimposed on solar X-ray images for the period 15–30 June 1973. Nearly all X-ray-emitting structures consist of systems of arches covering chromospheric neutral lines. Areas of low emissivity, coronal holes, appear as the areas between arcades of arches. The presence of a coronal hole, therefore, is determined by the spacing between neutral lines and the scale of the arches over those neutral lines. X-ray emissivity on the solar disk extends from neutral lines in proportion to the vertical and horizontal scale of the arches over those neutral lines. Increasing scale of arches corresponds with increasing age of magnetic fields associated with the neutral line. All X-ray filament cavities coincided with neutral lines, but filaments appeared under cavities for only part of their length and for only a fraction of the disk passage.A substantial portion of this work was done while a visitor at American Science and Engineering, Cambridge, Mass. 02139, U.S.A.     

Significance of boulder shape,shoreline configuration and pre-transport setting for the transport of boulders by tsunamis

Research on tsunami-induced coarse-clast transport is a field of rising interest since such deposits have been identified as useful proxies for extreme-wave events (tsunamis, storm waves) that provide crucial information for coastal hazard assessment. Physical experiments are, beside in-situ observations, the foundation of our understanding of how boulders are transported by tsunamis and provide clues to the development of empirical equations and numerical models describing the processes and fundamental mechanics. Nevertheless, investigating tsunami-induced boulder transport is a comparatively young discipline and only a few experimental studies focusing on this topic have been published so far. To improve the knowledge on nearshore tsunami hydrodynamics, physical experiments utilizing real-world boulder shapes have been carried out simulating three different shore types in a wave flume. Crucial insights were gained into boulder transport hydrodynamics and data resulting from the experiments were analysed in an empirical, statistical, quantitative and qualitative manner. The regular cuboid boulder – one of the specific shapes used in the experiments – showed the longest transport distances compared to a complex, natural boulder and a flat cuboid boulder, but also significant fluctuations regarding the total transport distance. The experiments indicate a strong influence of the shore shape on boulder transport behaviour. Experimental setups of increased mean transport distances also led to a higher spreading of results. This spreading was further amplified between the idealized-shaped cuboid and the complex-shaped boulder, which is associated with a lower drag coefficient. Due to the highly sensitive boulder reaction to divergent experimental setups, the need to recognize boundary conditions overcoming commonly considered parameters (e.g. roughness or Flatness Index) in field studies and numerical models is underlined. Beside the strong influence of initial boulder submergence and alignment, both the boulder shape and shore type influence the boulder transport pattern, increasing the total transport distance by more than 350% in some cases. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd