UV observations of the symbiotic star EG And

EG And is a S-type symbiotic star. Presented are UV observations made by IUE from 1978 to 1991. From these observations the electron density and the electron temperature were obtained. The size of the Heii emitting region was estimated as 7.3R. Line and continuum variations confirm the binary nature of EG And.     

A cosmological hydrodynamic code based on the piecewise parabolic method

We present a hydrodynamical code for cosmological simulations which uses the piecewise parabolic method (PPM) to follow the dynamics of the gas component and an N -body particle–mesh algorithm for the evolution of the collisionless component. The gravitational interaction between the two components is regulated by the Poisson equation which is solved by a standard fast Fourier transform (FFT) procedure. In order to simulate cosmological flows we have introduced several modifications to the original PPM scheme which we describe in detail. Various tests of the code are presented including adiabatic expansion, single and multiple pancake formation and three-dimensional cosmological simulations with initial conditions based on the cold dark matter scenario.     

On the MHD Acceleration of Astrophysical Jets

We present a 2.5D magnetohydrodynamic (MHD) simulation of the acceleration of a collimated jet from a magnetized accretion disk. We employ a MHD Adaptive Mesh Refinement (AMR) code (FLASH—University of Chicago). Thanks to this tool we can follow the evolution of the system for many dynamical timescales with a high-spatial resolution. Assuming an initial condition in which a Keplerian disk, thus with no accretion motions, is threaded by a uniform poloidal magnetic field, we show how both the accretion flow and the acceleration of the outflow occur, and we present in detail which are the forces responsible for the jet launching and collimation. Our simulation also shows how the collimating forces due to the self-generated toroidal magnetic field can produce some peculiar knotty features.     

On the stability of artificial equilibrium points in the circular restricted three-body problem

The article analyses the stability properties of minimum-control artificial equilibrium points in the planar circular restricted three-body problem. It is seen that when the masses of the two primaries are of different orders of magnitude, minimum-control equilibrium is obtained when the spacecraft is almost coorbiting with the second primary as long as their mutual distance is not too small. In addition, stability is found when the distance from the second primary exceeds a minimum value which is a simple function of the mass ratio of the two primaries and their separation. Lyapunov stability under non-resonant conditions is demonstrated using Arnold’s theorem. Among the most promising applications of the concept we find solar-sail-stabilized observatories coorbiting with the Earth, Mars, and Venus.     

Upslope-climbing shelf-edge clinoforms and the stepwise evolution of the northern European glaciation (lower Pleistocene Eridanos Delta system,U.K. North Sea): When sediment supply overwhelms accommodation

Clinoforms are basinward-dipping and accreting palaeo-bathymetric profiles that record palaeo-environmental conditions and processes; thus, clinothems represent natural palaeo-archives. Here, we document shelf-edge scale clinoform sets which prograded through the entire width of an epicontinental marine basin (ca. 400 km), eventually encroaching onto the opposite basin flank, where they started to prograde upslope and landward, in defiance of gravity (“upslope-climbing clinoforms”). The giant westward-prograding Eridanos muddy shelf-edge clinothem originated from the Baltic hinterland in the Oligocene and achieved maximum regression in the Early Pleistocene, on the UK Central Graben (CG) and Mid North Sea High (MNSH), after crossing the whole North Sea mesopelagic depocentre and causing near complete basin infill. Here we integrate well and seismic data through the MNSH and CG and examine the Eridanos final heyday and demise, identifying five clinothem complexes (A1, A2, A3, B and C) and six depositional sequence boundaries (SB1 to SB6) in the Miocene-Recent section. Tectonic and climatic events drove the recent evolution of this system. Early Pleistocene climate cooling, in particular, resulted in a stepwise increase in sediment supply. This climaxed in the earliest Calabrian, following a likely Eburonian eustatic fall (=SB3) when the Eridanos clastic wedge was restructured from a 100–300 m thick compound shelf-edge and delta system to a “hybrid” shelf-edge delta at sequence boundary SB3 (ca. 1.75 Ma). In the ca. 40 kyr that followed SB3, a progradation rate peak (>1,000 m/kyr) is associated with clinoforms starting to accrete upslope, onto the east-dipping slope between CG and MNSH. This “upslope-climbing clinoform” phase was quickly followed by the maximum regression and final retreat of the Eridanos system in the Early Calabrian (=SB4), likely as the result of climate-driven changes in the Baltic hinterland and/or delta auto-retreat. To our knowledge, this contributions represents the first documentation of “upslope-climbing clinoforms” recorded in the stratigraphic record.     

Biomass composition and methods for the determination of metabolic reserve polymers in phototrophic sulfur bacteria

To study nutrient fluxes within aquatic ecosystems, the synthesis of biomass and of various storage polymers has been analysed in samples from a meromictic alpine lake. Methods are described for the quantitative determination of whole cell biomass, glycogen, polyhydroxyalkanoates (PHA) and sulfur. Methods were adapted to conditions present in natural environments and tested with samples from blooms of Chromatiaceae and with corresponding laboratory cultures. Dried bacterioplankton-biomass has been analyzed for sulfur, glycogen and polyhydroxyalkanoates, and after complete oxidation for SO ₄ ^2- , NO ₃ ^- and HPO ₄ ^2- . The average elemental composition of biomass from phototrophic sulfur bacteria, depleted of sulfur and carbon storage compounds, was C₃₈₀H₅₈₀O₁₅₃N₆₇P₃S_2.5M, where M stands for the content of the remaining minor elements. C, H, O, N, P and S accounted for 86.7% of the total dry mass. Storage sulfur in natural populations was equivalent to 2.5% to 13.5% of the dry mass; its content varied by 80% within a diurnal cycle. Glycogen contents fluctuated by approximately 50%; they accounted for 7.5% to 15.2% of the dry cell mass. The total content of reserve materials per cell never exceeded 30% of the dry mass. PHA had not been found in appreciable amounts in cells harvested from the natural lake habitat. Under certain conditions in the laboratoryChromatium okenii could be induced, however, to produce polyhydroxyalkanoates. Sulfur, glycogen and PHA contents of 33, 26 and 11%, respectively, were achieved under laboratory-culture conditions. Cells with up to 60% of their dry mass consisting of reserve materials can be obtained under selected laboratory conditions.     

Analysis of macroseismic fields using statistical data depth functions: considerations leading to attenuation probabilistic modelling

Modelling seismic attenuation is one of the most critical points in the hazard assessment process. In this article we consider the spatial distribution of the effects caused by an earthquake as expressed by the values of the macroseismic intensity recorded at various locations surrounding the epicentre. Considering the ordinal nature of the intensity, a way to show its decay with distance is to draw curves—isoseismal lines—on maps, which bound points of intensity not smaller than a fixed value. These lines usually take the form of closed and nested curves around the epicentre, with highly different shapes because of the effects of ground conditions and of complexities in rupture propagation. Forecasting seismic attenuation of future earthquakes requires stochastic modelling of the decay on the basis of a common spatial pattern. The aim of this study is to consider a statistical methodology that identifies a general shape, if it exists, for isoseismal lines of a set of macroseismic fields. Data depth is a general nonparametric method for analysis of probability distributions and datasets. It has arisen as a statistical method to order points of a multivariate space, e.g., Euclidean space \({\mathbb {R}}^{p}\), \(p \ge 1\), according to the centrality with respect to a distribution or a given data cloud. Recently, this method has been extended to the ordering of functions and trajectories. In our case, for a fixed intensity decay \(\varDelta I\), we build a set of convex hulls that enclose the sites of felt intensity \(I_s \ge I_0 -\varDelta I\), one for each macroseismic field of a set of earthquakes that are considered as similar from the attenuation point of view. By applying data depth functions to this functional dataset, it is possible to identify the most central curve, i.e., the attenuation pattern, and to consider other properties like variability, outlyingness, and possible clustering of such curves. Results are shown for earthquakes that occurred on the Central Po Plain in May 2012, and on the eastern flank of Mt. Etna since 1865.     

The seismogenic thickness in Italy: constraints on potential magnitude and seismic hazard

The thickness of the seismogenic layer is a key parameter for seismic hazard, since it can be used to constrain the maximum depth of faulting and the potential magnitude. In this study, we compute the seismogenic thickness in the Italian region by defining the lower seismicity cut‐off, using high‐quality hypocentral locations of earthquakes that occurred in the past decade. Along the eastern Alps, the seismogenic thickness is about 12–14 km, laterally homogeneous along the entire south‐verging thrust front. In the Apennines extensional belt, lateral changes in seismogenic thickness are evident, and correlate with changes in the seismic energy released by past earthquakes. The potential magnitude is larger in the southern Apennines where the seismogenic thickness is greater (16–18 km) than in the northern Apennines where it is less (6–10 km) and seismic energy is partially released by the creeping of faults.     

Temperature dependence of goethite dissolution promoted by trihydroxamate siderophores

This article reports an investigation of the temperature dependence of goethite dissolution kinetics in the presence of desferrioxamine B (DFO-B), a trihydroxamate siderophore, and its acetyl derivative, desferrioxamine D1 (DFO-D1). At 25 and 40°C, DFO-D1 dissolved goethite at twice the rate of DFO-B, whereas at 55°C, the behavior of the two ligands was almost the same. Increasing the temperature from 25 to 55°C caused little or no significant change in DFO-B or DFO-D1 adsorption by goethite. A pseudo-first-order rate coefficient for dissolution, calculated as the ratio of the mass-normalized dissolution rate coefficient to the surface excess of siderophore, was approximately the same at 25 and 40°C for both siderophores. At 55°C, however, this rate coefficient for DFO-D1 was about half that for DFO-B. Analysis of the temperature dependence of the mass-normalized dissolution rate coefficient via the Arrhenius equation led to an apparent activation energy that was larger for DFO-B than for DFO-D1, but much smaller than that reported for the proton-promoted dissolution of goethite. A compensation law was found to relate the pre-exponential factor to the apparent activation energy in the Arrhenius equation, in agreement with what has been noted for the proton-promoted dissolution of oxide minerals and for the complexation of Fe³⁺ by DFO-B and simple hydroxamate ligands in aqueous solution. Analysis of these results suggested that the siderophores adsorb on goethite with a only single hydroxamate group in bidentate ligation with an Fe(III) center.