Melting and metallization of silica in the cores of gas giants, ice giants and super Earths

The physical state and properties of silicates at conditions encountered in the cores of gas giants, ice giants and of Earth like exoplanets now discovered with masses up to several times the mass of the Earth remains mostly unknown. Here, we report on theoretical predictions of the properties of silica, SiO$_2$, up to 4 TPa and about 20,000K using first principle molecular dynamics simulations based on density functional theory. For conditions found in the Super-Earths and in ice giants, we show that silica remains a poor electrical conductor up to 10 Mbar due to an increase in the Si-O coordination with pressure. For Jupiter and Saturn cores, we find that MgSiO$_3$ silicate has not only dissociated into MgO and SiO$_2$, as shown in previous studies, but that these two phases have likely differentiated to lead to a core made of liquid SiO$_2$ and solid (Mg,Fe)O.Comment: 5 pages, 4 figure

Recent advances in laser-plasma experiments using foams

The paper discusses recent advances in the use of foams in laser–plasma experiments, concerning in particular: (1) the use of foam in order to get an efficient smoothing of laser energy deposition, (2) the problem of hydrodynamics of layered foam-payload targets, (3) the use of foam for shock pressure amplification in equation-of-state experiments, (4) the study of the equation of state of foams in the Megabar regime, and (5) the use of foams for astrophysics relevant experiments, here in particular shock acceleration experiments

Delayed nipple-sparing modified subcutaneous mastectomy: Rationale and technique

The problem of nipple-areola complex (NAC) preservation during mastectomy is a very intriguing and stimulating issue. In fact, in order to perform an oncologically safe operation, no mammary tissue (enclosed in the main galactophoric ducts) should remain; on the other hand, without the blood supply coming from the breast gland, NAC viability is greatly impaired because the surrounding vascular dermal network is not developed enough to support its metabolic requirements. We suggest therefore a two-step surgical procedure. The first step, on an outpatient basis with local tumescent anesthesia, is a mini-invasive cutting and coagulating procedure. It addresses the autonomization of the vascular supply to the NAC by detaching the galactophore stalk from the nipple and coagulating the deep vascular plexus. The second step, under general anesthesia and again with tumescent technique, removes the breast within its capsule, with careful checks of any remnant and adequate approach to the axilla. A subpectoralis prosthesis completes the procedure. In our view, this technique is electively suitable for prophylactic mastectomy, but also for stage I breast cancer, 2.5 cm from the NAC and 1.5 cm from the skin and pectoralis fascia, and it is very safe, simple, and effective

Eliciting Implicit Awareness in Alzheimer’s Disease and Mild Cognitive Impairment: A Task-Based Functional MRI Study

Background: Recent models of anosognosia in dementia have suggested the existence of an implicit component of self-awareness about one’s cognitive impairment that may remain preserved and continue to regulate behavioral, affective, and cognitive responses even in people who do not show an explicit awareness of their difficulties. Behavioral studies have used different strategies to demonstrate implicit awareness in patients with anosognosia, but no neuroimaging studies have yet investigated its neural bases. Methods: Patients with amnestic mild cognitive impairment and dementia due to Alzheimer’s disease underwent functional magnetic resonance imaging (fMRI) during the execution of a color-naming task in which they were presented with neutral, negative, and dementia-related words (Dementia-Related Emotional Stroop). Results: Twenty-one patients were recruited: 12 were classified as aware and 9 as unaware according to anosognosia scales (based on clinical judgment and patient-caregiver discrepancy). Behavioral results showed that aware patients took the longest time to process dementia-related words, although differences between word types were not significant, limiting interpretation of behavioral results. Imaging results showed that patients with preserved explicit awareness had a small positive differential activation of the posterior cingulate cortex (PCC) for the dementia-related words condition compared to the negative words, suggesting attribution of emotional valence to both conditions. PCC differential activation was instead negative in unaware patients, i.e., lower for dementia-related words relative to negative-words. In addition, the more negative the differential activation, the lower was the Stroop effect measuring implicit awareness. Conclusion: Posterior cingulate cortex preserved response to dementia-related stimuli may be a marker of preserved implicit self-awareness

Design of absolute equation of state measurements in optically thick materials by laser-driven shock waves

Abstract Some aspects of the design of a target for the absolute measurement of Equation-of-State data at pressure of tens of Mbar, in optically thick materials are discussed. In the proposed experiment, a shock wave is generated in a laser-irradiated sample, and the shock velocity and the material velocity behind the shock are simultaneously measured by the optical and X-ray diagnostics. Accurate measurements require the generation of a steady, planar shock, and the detection of the motion of a shocked fluid interface by transverse radiography. One- and two-dimensional numerical fluid simulations have been performed to optimize beam and target design, in order to fulfil such requirements

Simulation of preheating effects in shock wave experiments

We have analyzed the shock wave propagation experiments performed at LULI and presented at ECLIM'94. The targets were aluminium foils with thickness from 5 to 25 μm. Simulations were performed with the SARA-1D multigroup radiation code. We have shown a small level of preheating caused by the absorption of X-rays with energies close to the K-edge of aluminum. Several sets of opacities were used in order to study this effect, including experimental values for cold aluminum. Simulations show a small level of visible emission induced by X-ray preheating before the arrival of the shock

Decaying shock studies of phase transitions in MgOSiO2 systems: implications for the Super-Earths interiors

We report an experimental study of the phase diagrams of periclase (MgO), enstatite (MgSiO3) and forsterite (Mg2SiO4) at high pressures. We investigated with laser driven decaying shocks the pressure/temperature curves of MgO, MgSiO3 and Mg2SiO4 between 0.2-1.2 TPa, 0.12-0.5 TPa and 0.2-0.85 TPa respectively. A melting signature has been observed in MgO at 0.47 TPa and 9860 K, while no phase changes were observed neither in MgSiO3 nor in Mg2SiO4. An increasing of reflectivity of MgO, MgSiO3 and Mg2SiO4 liquids have been detected at 0.55 TPa -12 760 K, 0.15 TPa - 7540 K, 0.2 TPa - 5800 K, respectively. In contrast to SiO2, melting and metallization of these compounds do not coincide implying the presence of poor electrically conducting liquids close to the melting lines. This has important implications for the generation of dynamos in Super-earths mantles