The Role of Solar Wind Structures in the Generation of ULF Waves in the Inner Magnetosphere

The plasma of the solar wind incident upon the Earth’s magnetosphere can produce several types of geoeffective events. Among them, an important phenomenon consists of the interrelation of the magnetospheric–ionospheric current systems and the charged-particle population of the Earth’s Van Allen radiation belts. Ultra-low-frequency (ULF) waves resonantly interacting with such particles have been claimed to play a major role in the energetic particle flux changes, particularly at the outer radiation belt, which is mainly composed of electrons at relativistic energies. In this article, we use global magnetohydrodynamic simulations along with in situ and ground-based observations to evaluate the ability of two different solar wind transient (SWT) events to generate ULF (few to tens of mHz) waves in the equatorial region of the inner magnetosphere. Magnetic field and plasma data from the Advanced Composition Explorer (ACE) satellite were used to characterize these two SWT events as being a sector boundary crossing (SBC) on 24 September 2013, and an interplanetary coronal mass ejection (ICME) in conjunction with a shock on 2 October 2013. Associated with these events, the twin Van Allen Probes measured a depletion of the outer belt relativistic electron flux concurrent with magnetic and electric field power spectra consistent with ULF waves. Two ground-based observatories apart in 90^° longitude also showed evidence of ULF-wave activity for the two SWT events. Magnetohydrodynamic (MHD) simulation results show that the ULF-like oscillations in the modeled electric and magnetic fields observed during both events are a result from the SWT coupling to the magnetosphere. The analysis of the MHD simulation results together with the observations leads to the conclusion that the two SWT structures analyzed in this article can be geoeffective on different levels, with each one leading to distinct ring current intensities, but both SWTs are related to the same disturbance in the outer radiation belt, i.e. a dropout in the relativistic electron fluxes. Therefore, minor disturbances in the solar wind parameters, such as those related to an SBC, may initiate physical processes that are able to be geoeffective for the outer radiation belt.     

The role of the background in past and future X-ray missions

Background has played an important role in X-ray missions, limiting the exploitation of science data in several and sometimes unexpected ways. In this presentation I review past X-ray missions focusing on some important lessons we can learn from them. I then go on discussing prospects for overcoming background related limitations in future ones.     

Constraining the pass-band of future space-based coronagraphs for observations of solar eruptions in the FeXIV 530.3 nm “green line”

Observations of the solar corona in the FeXIV 530.3 nm “green line” have been very important in the past, and are planned for future coronagraphs on-board forthcoming space missions such as PROBA-3 and Aditya. For these instruments, a very important parameter to be optimized is the spectral width of the band-pass filter to be centred over the “green line”. Focusing on solar eruptions, motions occurring along the line of sight will Doppler shift the line profiles producing an emission that will partially fall out of the narrower pass-band, while broader pass-band will provide observations with reduced spectral purity. To address these issues, we performed numerical (MHD) simulation of CME emission in the “green line” and produced synthetic images assuming 4 different widths of the pass-band (Δλ = 20 Å, 10 Å, 5 Å, and 2 Å). It turns out that, as expected, during solar eruptions a significant fraction of “green line” emission will be lost using narrower filters; on the other hand these images will have a higher spectral purity and will contain emission coming from parcels of plasma expanding only along the plane of the sky. This will provide a better definition of single filamentary features and will help isolating single slices of plasma through the eruption, thus reducing the problem of superposition of different features along the line of sight and helping physical interpretation of limb events. For these reasons, we suggest to use narrower band passes (Δλ ≤ 2 Å) for the observations of solar eruptions with future coronagraphs.     

Influence of different mechanical column-foundation connection devices on the seismic behaviour of precast structures

Dry-assembled precast concrete frame structures are typically made with dowel beam-to-column connections, which allow relative rotation along the beam direction. In the orthogonal direction the rotation of the beam is prevented but again the connections of the superimposed floor elements allow for relative rotation. All the ductility and energy dissipation demand in case of seismic action is therefore concentrated at the base of cantilever columns. Hence, the column-to-foundation connection plays a key role on the seismic performance of such structures. Mechanical connection devices, even if correctly designed for what concerns resistance, may affect the behaviour of the whole joint modifying the ductility capacity of the columns and their energy dissipation properties. An experimental campaign on different mechanical connection devices has been performed at Politecnico di Milano within the Safecast project (European programme FP7-SME-2007-2, Grant agreement No. 218417, 2009). The results of cyclic tests on full scale structural sub-assembly specimens are presented. Design rules are suggested for each of the tested connections on the basis of the experimental observations, and numerical analyses have been performed with hysteretic parameters calibrated on the experimental loops. The seismic performance of structures provided with those connections is investigated through a case study on a multi-storey precast building prototype, which has also been subject to full-scale pseudo-dynamic testing within the same research project at the European Laboratory of Structural Assessment of the Joint Research Centre of the European Commission. The comparison of the results from the structure provided with the different studied connections clearly highlights how some solutions may lead to both reduction of ductility capacity and dissipation of energy, increasing the expected structural damage and the seismic risk.     

Space and time variability of uncertainty in morphodynamic simulations

The uncertainty associated with simulations of process-based coastal area morphodynamic models is assessed through numerical experimentation. Appropriate metrics of uncertainty are defined based on the standard deviation of the model results at each location and each time step. Uncertainty is examined using a set of realistic one year morphodynamic simulations of the evolution of a highly dynamic tidal inlet. Results indicate that uncertainty increases linearly with time, and suggest that its rate grows with increasing sediment fluxes. Hence, the limits of predictability of morphodynamic model applications are higher for slowly varying systems. Attempts to reduce uncertainty by aggregating model results at larger spatial scales met with limited success. Ensemble simulations are suggested as a possible avenue to investigate the long-term evolution of tidal inlets using process-based models.     

Removal of Lead, Copper, Zinc and Cadmium from Water Using Phosphate Rock

Removal of Pb2 ,Cu~(2 ),Zn~(2 )and Cd~(2 )from aqueous solutions by sorption on a natural phosphate rock(FAP)was investigated.The effects of the contact time and initial metal concentration were examined in the batch method.The percentage sorption of heavy metals from solution ranges generally between 50% and 99%.The amount of sorbed metal ions follows the order Cu>Pb>Cd>Zn. Heavy metal immobilization was attributed to both surface complexation of metal ions on the surface of FAP grains and partial dissolution and precipitation of a heavy metal-containing phosphate.The very low desorption ratio of heavy metals further supports the effectiveness of FAP as an alternative and low-cost material to remove toxic Pb~(2 ),Cu~(2 ),Zn~(2 )and Cd~(2 )from polluted waters.     

Exploiting the use of physical information for the calibration of a lumped hydrological model

In hydrological modelling, the challenge is to identify an optimal strategy to exploit tools and available observations in order to enhance model reliability. The increasing availability of data promotes the use of new calibration techniques able to make use of additional information on river basins. In the present study, a lumped hydrological model—designed with the aim of utilizing remotely sensed data—is introduced and calibrated, adopting four different schemes that adopt, to varying extents, available physical information. The physically consistent conceptualization of the hydrological model used allowed development of a step by step calibration based on a combination of information, such as remotely sensed data describing snow cover, recession curves obtained from streamflow measurements, and time series of surface run‐off obtained with a baseflow mathematical filter applied to the streamflow time‐series. Results suggest that the use of physical information in the calibration procedure tends to increase model reliability with respect to approaches where the parameters are calibrated using an overall statistic based, considerably or exclusively, on streamflow data.     

Refining image-velocimetry performances for streamflow monitoring: Seeding metrics to errors minimization

River streamflow monitoring is currently facing a transformation due to the emerging of new innovative technologies. Fixed and mobile measuring systems are capable of quantifying surface flow velocities and discharges, relying on video acquisitions. This camera-gauging framework is sensitive to what the camera can “observe” but also to field circumstances such as challenging weather conditions, river background transparency, transiting seeding characteristics, among others. This short communication paper introduces the novel idea of optimizing image velocimetry techniques selecting the most informative sequence of frames within the available video. The selection of the optimal frame window is based on two reasonable criteria: (a) the maximization of the number of frames, subject to (b) the minimization of the recently introduced dimensionless seeding distribution index (SDI). SDI combines seeding characteristics such as seeding density and spatial clustering of tracers, which are used as a proxy to enhance the reliability of image velocimetry techniques. Two field case studies were considered as a proof-of-concept of the proposed framework, on which seeding metrics were estimated and averaged in time to select the proper application window. The selected frames were analysed using LSPIV to estimate the surface flow velocities and river discharge. Results highlighted that the proposed framework might lead to a significant error reduction. In particular, the computed discharge errors, at the optimal portion of the footage, were about 0.40% and 0.12% for each case study, respectively. These values were lower than those obtained, considering all frames available.     

A systematic analysis of the XMM-Newton background: III. Impact of the magnetospheric environment

A detailed characterization of the particle induced background is fundamental for many of the scientific objectives of the Athena X-ray telescope, thus an adequate knowledge of the background that will be encountered by Athena is desirable. Current X-ray telescopes have shown that the intensity of the particle induced background can be highly variable. Different regions of the magnetosphere can have very different environmental conditions, which can, in principle, differently affect the particle induced background detected by the instruments. We present results concerning the influence of the magnetospheric environment on the background detected by EPIC instrument onboard XMM-Newton through the estimate of the variation of the in-Field-of-View background excess along the XMM-Newton orbit. An important contribution to the XMM background, which may affect the Athena background as well, comes from soft proton flares. Along with the flaring component a low-intensity component is also present. We find that both show modest variations in the different magnetozones and that the soft proton component shows a strong trend with the distance from Earth.     

Conceptual design and full‐scale experimentation of cladding panel connection systems of precast buildings

Despite the long series of European research projects that has led to the setting of fully reliable seismic design criteria for precast structures, recent earthquakes have shown that a weak point still exists in the proportioning of the connection systems of cladding wall panels. Following this finding, this paper outlines an organic setting of the design problem of precast concrete structures including cladding–structure interaction and describes three possible solutions, namely, the isostatic, integrated, and dissipative systems. The related fastening arrangements, with the use of existing and innovative connection devices, are also described. This paper comments on the results of the pseudo‐dynamic and cyclic tests performed at ELSA Laboratory of the European Joint Research Centre of Ispra (Italy) on a full‐scale prototype of precast structure. The conception and the experimental performance of the structure with nine different configurations of either vertical or horizontal wall panel claddings are presented. The analysis of the results highlights the effectiveness of the different solutions in a comparative way. Copyright © 2017 John Wiley & Sons, Ltd.