SILICATE NANOPARTICLES PRODUCED BY LABORATORY SIMULATED SPACE WEATHERING OF OLIVINE SINGLE CRYSTALS

Silicate nanoparticles, otherwise referred to as very small grains (VSGs) [1], occur in the interstellar medium. These grains experience a strong structural modification during their lifetime in the diffuse interstellar medium, due to events such as grain-grain collisions and irradiation. Grain amorphization is one of the major effects, transforming crystalline dust concentrated in star envelopes into amorphous silicate grains populating the interstellar medium [2]. Moreover, several studies have pointed out that the main building blocks of these silicates are O, Si, Fe, Mg, Al and Ca, all elements that are among the principal constituents of the Earth’s surface [3], thus leading to the name “astronomical silicates”. However, the structure and chemical evolution together with the origin of these grains are still poorly understood and intensively debated [4,5]. The aim of this study is the simulation of space weathering processes by liquid phase pulsed laser ablation (LP-PLA) on olivine single crystals. We adopt a multiple technique characterization, taking advantage of optical spectroscopy analyses and high- resolution transmission electron microscopy (HR-TEM), to shed light on the structure and chemical evolution of the ablated material

Astronomical silicate nanoparticle analogues produced by pulsed laser ablation on olivine single crystals

Silicate nanoparticles, otherwise referred to as very small grains (VSGs) [1], occur in various astrophysical environments. These grains experience substantial processing (e.g., amorphization) during their lifetime in the diffuse interstellar medium due to events such as grain-grain collisions and irradiation [2]. Moreover, several studies have pointed out that the main building blocks of these silicates are O, Si, Fe, Mg, Al and Ca, all elements that are among the principal constituents of the Earth’s surface [3], thus leading to the name “astronomical silicates”. However, the structure and chemical evolution together with the origin of these grains are still poorly understood and intensively debated [4,5]. The aim of this study is the simulation of space weathering processes on olivine single crystals by liquid phase pulsed laser ablation (LP-PLA). The study of the resulting structure of both the target and the ablated material together with their chemical evolution has been carried out by a multiple technique characterization. In particular, spectroscopy and dynamic light scattering measurements, analyses of the electrostatic properties and reactivity to acids and bases on the obtained colloidal solutions of the ablated nanoproducts have been performed and coupled with highresolution transmission electron microscopy (HR-TEM). Selected olivine target crystals (Fo87) from the São Miguel island (Azores) were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). LP-PLA experiments were performed with a Nd:YAG laser focused via a singlet lens onto the surface of the target, which was fixed at the bottom of a polystyrene box filled with 4 ml of deionized water (type 1) to immerge it completely. Laser pulses of 5 ns and 100 mJ simulate the timeframe and energy exchange occurring during grain-grain interstellar collisions [6] and they generate a plasma plume at the crystal/liquid interface. The rapid cooling induced by the confining liquid layer brings about the condensation of the chemical vapor it contains with production of a colloidal solution of nanoparticles. These solutions were analyzed by dynamic light scattering techniques and optical absorption spectroscopy in the range from 200 nm to 1100 nm (6.20 eV - 1.13 eV). Absorption measurements on the colloidal solutions have been compared against reference colloidal solutions dispersed in deionized water (i.e. mesoporous silica [SiO2] nanoparticles, brucite [Mg(OH)2] nanoparticles, aluminum hydroxide [Al(OH)3] nanoparticles, chrysotile [Mg3Si2O5(OH)4] nanotubes, and synthetic forsterite [Mg2SiO4] nanoparticles). Moreover, additional absorption analyses have been carried out as a function of the addition of known aliquots of sulfuric acid and sodium hydroxide solutions. TEM/EDS analyses were then performed on the ablated nanoparticles deposited via electrophoresis on C-coated Cu grids and compositional variations of the ablated target were determined by X-ray photo-emission spectroscopy analyses. The size distribution of LP-PLA synthesized nanoparticles is typically multimodal due to aggregation phenomena. Aggregation is consistent with the measured ζ-potential, which is negative with a relatively low absolute value, within the range 30-50 mV. Nonetheless, a recurrent mode is centered at about 2 nm (hydrodynamic diameter) and it is consistent with the measured size distribution obtained by transmission electron microscopy analysis (average nanoparticles diameter around 3-5 nm). Optical absorption measurements on the ejected material show a main band around 215 nm. This feature is very similar to the “B2 band” reported in several studies on silica glass [7] and ascribed to oxygen vacancies, but its nature is still far to be fully understood. We also found that this feature at 215 nm is very common among both Si and Mg compounds (e.g., Sioxide, Mg-hydroxide, chrysotile). Moreover, additional absorption bands in the range 240-350nm are observed suggesting the formation of new space weathering products as result of the ablation process. Therefore, these results suggest that substantial chemical processing might be expected during space weathering of “typical” interstellar grains into VSGs. Moreover, coupling these experimental results with remote sensing datasets will provide fundamental information about the origin and evolution of these silicate grains

Intraspecies Transmission of BASE Induces Clinical Dullness and Amyotrophic Changes

The disease phenotype of bovine spongiform encephalopathy (BSE) and the molecular/ biological properties of its prion strain, including the host range and the characteristics of BSE-related disorders, have been extensively studied since its discovery in 1986. In recent years, systematic testing of the brains of cattle coming to slaughter resulted in the identification of at least two atypical forms of BSE. These emerging disorders are characterized by novel conformers of the bovine pathological prion protein (PrPTSE), named high-type (BSE-H) and low-type (BSE-L). We recently reported two Italian atypical cases with a PrPTSE type identical to BSE-L, pathologically characterized by PrP amyloid plaques and known as bovine amyloidotic spongiform encephalopathy (BASE). Several lines of evidence suggest that BASE is highly virulent and easily transmissible to a wide host range. Experimental transmission to transgenic mice overexpressing bovine PrP (Tgbov XV) suggested that BASE is caused by a prion strain distinct from the BSE isolate. In the present study, we experimentally infected Friesian and Alpine brown cattle with Italian BSE and BASE isolates via the intracerebral route. BASE-infected cattle developed amyotrophic changes accompanied by mental dullness. The molecular and neuropathological profiles, including PrP deposition pattern, closely matched those observed in the original cases. This study provides clear evidence of BASE as a distinct prion isolate and discloses a novel disease phenotype in cattle

Effect of the relative shift between the electron density and temperature pedestal position on the pedestal stability in JET-ILW and comparison with JET-C

The electron temperature and density pedestals tend to vary in their relative radial positions, as observed in DIII-D (Beurskens et al 2011 Phys. Plasmas 18 056120) and ASDEX Upgrade (Dunne et al 2017 Plasma Phys. Control. Fusion 59 14017). This so-called relative shift has an impact on the pedestal magnetohydrodynamic (MHD) stability and hence on the pedestal height (Osborne et al 2015 Nucl. Fusion 55 063018). The present work studies the effect of the relative shift on pedestal stability of JET ITER-like wall (JET-ILW) baseline low triangularity (\u3b4) unseeded plasmas, and similar JET-C discharges. As shown in this paper, the increase of the pedestal relative shift is correlated with the reduction of the normalized pressure gradient, therefore playing a strong role in pedestal stability. Furthermore, JET-ILW tends to have a larger relative shift compared to JET carbon wall (JET-C), suggesting a possible role of the plasma facing materials in affecting the density profile location. Experimental results are then compared with stability analysis performed in terms of the peeling-ballooning model and with pedestal predictive model EUROPED (Saarelma et al 2017 Plasma Phys. Control. Fusion). Stability analysis is consistent with the experimental findings, showing an improvement of the pedestal stability, when the relative shift is reduced. This has been ascribed mainly to the increase of the edge bootstrap current, and to minor effects related to the increase of the pedestal pressure gradient and narrowing of the pedestal pressure width. Pedestal predictive model EUROPED shows a qualitative agreement with experiment, especially for low values of the relative shift

The treatment of irreparable massive rotator cuff tears with inspace balloon: rational and medium-term results

The treatment of irreparable massive rotator cuff tears (MIRCTs) represents a challenge for the orthopedic surgeon both for the affected population and for the intrinsic characteristics of the injury. There are different types of treatment ranging from bursectomy to reverse shoulder prosthesis and subacromial spacers. The aim of the work is to establish the clinical and functional improvement of patients treated with subacromial spacer

Myocardial dysfunction and adrenergic cardiac innervation in patients with insulin-dependent diabetes mellitus

IF 7.06