Erratum: Delayed Onset of Nonthermal Melting in Single-Crystal Silicon Pumped with Hard X Rays [Phys. Rev. Lett. 120, 265701 (2018)].

This corrects the article DOI: 10.1103/PhysRevLett.120.265701.

Identification of Phase Transitions and Metastability in Dynamically Compressed Antimony Using Ultrafast X-Ray Diffraction.

Ultrafast x-ray diffraction at the LCLS x-ray free electron laser has been used to resolve the structural behavior of antimony under shock compression to 59 GPa. Antimony is seen to transform to the incommensurate, host-guest phase Sb-II at ∼11 GPa, which forms on nanosecond timescales with ordered guest-atom chains. The high-pressure bcc phase Sb-III is observed above ∼15 GPa, some 8 GPa lower than in static compression studies, and mixed Sb-III/liquid diffraction are obtained between 38 and 59 GPa. An additional phase which does not exist under static compression, Sb-I^{'}, is also observed between 8 and 12 GPa, beyond the normal stability field of Sb-I, and resembles Sb-I with a resolved Peierls distortion. The incommensurate Sb-II high-pressure phase can be recovered metastably on release to ambient pressure, where it is stable for more than 10 ns.

Delayed Onset of Nonthermal Melting in Single-Crystal Silicon Pumped with Hard X Rays.

In this work, we monitor the onset of nonthermal melting in single-crystal silicon by implementing an x-ray pump-x-ray probe scheme. Using the ultrashort pulses provided by the Linac Coherent Light Source (SLAC) and a custom-built split-and-delay line for hard x rays, we achieve the temporal resolution needed to detect the onset of the transition. Our data show no loss of long-range order up to 150±40 fs from photoabsorption, which we interpret as the time needed for the electronic system to equilibrate at or above the critical nonthermal melting temperature. Once such equilibration is reached, the loss of long-range atomic order proceeds inertially and is completed within 315±40 fs from photoabsorption.

Compression Freezing Kinetics of Water to Ice VII.

Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6 nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. These first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

Ultrafast X-Ray Diffraction Studies of the Phase Transitions and Equation of State of Scandium Shock Compressed to 82 GPa.

Using x-ray diffraction at the Linac Coherent Light Source x-ray free-electron laser, we have determined simultaneously and self-consistently the phase transitions and equation of state (EOS) of the lightest transition metal, scandium, under shock compression. On compression scandium undergoes a structural phase transition between 32 and 35 GPa to the same bcc structure seen at high temperatures at ambient pressures, and then a further transition at 46 GPa to the incommensurate host-guest polymorph found above 21 GPa in static compression at room temperature. Shock melting of the host-guest phase is observed between 53 and 72 GPa with the disappearance of Bragg scattering and the growth of a broad asymmetric diffraction peak from the high-density liquid.

Dynamic compression of water to conditions in ice giant interiors.

Recent discoveries of water-rich Neptune-like exoplanets require a more detailed understanding of the phase diagram of H2O at pressure-temperature conditions relevant to their planetary interiors. The unusual non-dipolar magnetic fields of ice giant planets, produced by convecting liquid ionic water, are influenced by exotic high-pressure states of H2O-yet the structure of ice in this state is challenging to determine experimentally. Here we present X-ray diffraction evidence of a body-centered cubic (BCC) structured H2O ice at 200 GPa and ~ 5000 K, deemed ice XIX, using the X-ray Free Electron Laser of the Linac Coherent Light Source to probe the structure of the oxygen sub-lattice during dynamic compression. Although several cubic or orthorhombic structures have been predicted to be the stable structure at these conditions, we show this BCC ice phase is stable to multi-Mbar pressures and temperatures near the melt boundary. This suggests variable and increased electrical conductivity to greater depths in ice giant planets that may promote the generation of multipolar magnetic fields.

Atomistic deformation mechanism of silicon under laser-driven shock compression.

Silicon (Si) is one of the most abundant elements on Earth, and it is the most widely used semiconductor. Despite extensive study, some properties of Si, such as its behaviour under dynamic compression, remain elusive. A detailed understanding of Si deformation is crucial for various fields, ranging from planetary science to materials design. Simulations suggest that in Si the shear stress generated during shock compression is released via a high-pressure phase transition, challenging the classical picture of relaxation via defect-mediated plasticity. However, direct evidence supporting either deformation mechanism remains elusive. Here, we use sub-picosecond, highly-monochromatic x-ray diffraction to study (100)-oriented single-crystal Si under laser-driven shock compression. We provide the first unambiguous, time-resolved picture of Si deformation at ultra-high strain rates, demonstrating the predicted shear release via phase transition. Our results resolve the longstanding controversy on silicon deformation and provide direct proof of strain rate-dependent deformation mechanisms in a non-metallic system.

Carbon clusters formed from shocked benzene.

Benzene (C6H6), while stable under ambient conditions, can become chemically reactive at high pressures and temperatures, such as under shock loading conditions. Here, we report in situ x-ray diffraction and small angle x-ray scattering measurements of liquid benzene shocked to 55 GPa, capturing the morphology and crystalline structure of the shock-driven reaction products at nanosecond timescales. The shock-driven chemical reactions in benzene observed using coherent XFEL x-rays were a complex mixture of products composed of carbon and hydrocarbon allotropes. In contrast to the conventional description of diamond, methane and hydrogen formation, our present results indicate that benzene's shock-driven reaction products consist of layered sheet-like hydrocarbon structures and nanosized carbon clusters with mixed sp2-sp3 hybridized bonding. Implications of these findings range from guiding shock synthesis of novel compounds to the fundamentals of carbon transport in planetary physics.

Mercury and metal(loid) deposition to remote Nova Scotia lakes from both local and distant sources.

Kejimkujik National Park, in Nova Scotia, Canada, is a sensitive region for metal(loid) contamination, such as mercury, in part due to long-range atmospheric deposition from global and regional industrial centers. The region is remote from industrial centres, but is downwind of major pollution sources in the Eastern United States and Canada, and historically had numerous gold mining sites. Due to a paucity of long-term atmospheric deposition monitoring in this region, little is known about the response of Kejimkujik lakes to multiple changing global, regional and local atmospheric Hg and metal(loid) sources. Here, we used multiple lake sediment cores to reconstruct anthropogenic depositional fluxes of metal(loid)s of concern for the last ~210years. Results showed that Kejimkujik lake sediments are highly enriched in lead (Pb), antimony (Sb) and tin (Sn), with post-industrial metal(loid) concentrations being >4-fold greater than natural baseline levels (prior to ~1800) and moderately enriched in silver (Ag), bismuth (Bi), cadmium (Cd), copper (Cu), mercury (Hg), rubidium (Rb), tellurium (Te), thallium (Tl), vanadium (V), tungsten (W) and zinc (Zn), with post-industrial metal(loid) concentrations being between 1.5 and 4-fold greater than natural baseline levels (prior to ~1800). Lake sediment core reconstructions of total atmospheric Hg deposition matched well with Hg wet deposition monitoring data from the overlapped period (1997-2010) being 9.1±2.7µg/m2/yr and 7.0±0.7µg/m2/yr respectively. Lakes closest to historic gold mining sites show spikes in Ag, Cd, Sb, Tl, Zn and W during mining periods (~1880 and 1950). Most of the enriched metal(loid)s (EF >1.5) (Ag, Bi, Cu, Hg, Pb, Sb, Sn, V and W) do not appear affected by redox and remobilisation issues. For the other enriched metal(loid)s (EF >1.5) (Cd, Tl, and Zn), remobilisation from upper sediments appears to be occurring within these acidic and DOC rich Kejimkujik lakes.

Direct imaging of ultrafast lattice dynamics.

Under rapid high-temperature, high-pressure loading, lattices exhibit complex elastic-inelastic responses. The dynamics of these responses are challenging to measure experimentally because of high sample density and extremely small relevant spatial and temporal scales. Here, we use an x-ray free-electron laser providing simultaneous in situ direct imaging and x-ray diffraction to spatially resolve lattice dynamics of silicon under high-strain rate conditions. We present the first imaging of a new intermediate elastic feature modulating compression along the axis of applied stress, and we identify the structure, compression, and density behind each observed wave. The ultrafast probe x-rays enabled time-resolved characterization of the intermediate elastic feature, which is leveraged to constrain kinetic inhibition of the phase transformation between 2 and 4 ns. These results not only address long-standing questions about the response of silicon under extreme environments but also demonstrate the potential for ultrafast direct measurements to illuminate new lattice dynamics.

Femtosecond diffraction studies of solid and liquid phase changes in shock-compressed bismuth.

Bismuth has long been a prototypical system for investigating phase transformations and melting at high pressure. Despite decades of experimental study, however, the lattice-level response of Bi to rapid (shock) compression and the relationship between structures occurring dynamically and those observed during slow (static) compression, are still not clearly understood. We have determined the structural response of shock-compressed Bi to 68 GPa using femtosecond X-ray diffraction, thereby revealing the phase transition sequence and equation-of-state in unprecedented detail for the first time. We show that shocked-Bi exhibits a marked departure from equilibrium behavior - the incommensurate Bi-III phase is not observed, but rather a new metastable phase, and the Bi-V phase is formed at significantly lower pressures compared to static compression studies. We also directly measure structural changes in a shocked liquid for the first time. These observations reveal new behaviour in the solid and liquid phases of a shocked material and give important insights into the validity of comparing static and dynamic datasets.

Time-resolved diffraction of shock-released SiO2 and diaplectic glass formation.

Understanding how rock-forming minerals transform under shock loading is critical for modeling collisions between planetary bodies, interpreting the significance of shock features in minerals and for using them as diagnostic indicators of impact conditions, such as shock pressure. To date, our understanding of the formation processes experienced by shocked materials is based exclusively on ex situ analyses of recovered samples. Formation mechanisms and origins of commonly observed mesoscale material features, such as diaplectic (i.e., shocked) glass, remain therefore controversial and unresolvable. Here we show in situ pump-probe X-ray diffraction measurements on fused silica crystallizing to stishovite on shock compression and then converting to an amorphous phase on shock release in only 2.4 ns from 33.6 GPa. Recovered glass fragments suggest permanent densification. These observations of real-time diaplectic glass formation attest that it is a back-transformation product of stishovite with implications for revising traditional shock metamorphism stages.

Pressure-dependent isotopic composition of iron alloys.

Our current understanding of Earth's core formation is limited by the fact that this profound event is far removed from us physically and temporally. The composition of the iron metal in the core was a result of the conditions of its formation, which has important implications for our planet's geochemical evolution and physical history. We present experimental and theoretical evidence for the effect of pressure on iron isotopic composition, which we found to vary according to the alloy tested (FeO, FeH(x), or Fe3C versus pure Fe). These results suggest that hydrogen or carbon is not the major light-element component in the core. The pressure dependence of iron isotopic composition provides an independent constraint on Earth's core composition.

Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2.

Pressure- and temperature-induced phase transitions have been studied for more than a century but very little is known about the non-equilibrium processes by which the atoms rearrange. Shock compression generates a nearly instantaneous propagating high-pressure/temperature condition while in situ X-ray diffraction (XRD) probes the time-dependent atomic arrangement. Here we present in situ pump-probe XRD measurements on shock-compressed fused silica, revealing an amorphous to crystalline high-pressure stishovite phase transition. Using the size broadening of the diffraction peaks, the growth of nanocrystalline stishovite grains is resolved on the nanosecond timescale just after shock compression. At applied pressures above 18 GPa the nuclueation of stishovite appears to be kinetically limited to 1.4±0.4 ns. The functional form of this grain growth suggests homogeneous nucleation and attachment as the growth mechanism. These are the first observations of crystalline grain growth in the shock front between low- and high-pressure states via XRD.

Impaired affective prosody in AD: relationship to aphasic deficits and emotional behaviors.

OBJECTIVE: To assess the ability of patients with AD to produce, repeat, and comprehend affective prosody in relationship to severity of dementia, aphasic deficits, and changes in emotional behaviors. METHODS: An Aprosodia Battery was used to assess affective-prosodic performance and to identify patterns of deficits in affective communication. In addition, the presence and severity of aberrant behaviors, depression, and aphasia were assessed using standardized assessment tools. RESULTS: Patients with AD had significant impairments in their ability to repeat, comprehend, and discriminate affective aspects of speech, but maintained normal spontaneous affective-prosodic performances. As dementia severity increased, performance on the comprehension tasks and, to a lesser degree, on the repetition tasks became more impaired; spontaneous affective prosody remained normal. In the current study, affective-prosodic comprehension impairments were present in patients with all stages of AD; comparable aphasic deficits were not observed until patients were severely demented. The majority of aphasic deficits involved anomia without loss of comprehension. Patients with AD with sensory aprosodia had increased frequency and severity of behavioral changes whereas patients with AD with normal affective-prosodic performance were significantly less demented, had normal linguistic ability, and displayed fewer aberrant psychiatric behaviors. CONCLUSION: Patients with mild AD are at considerable risk for affective-prosodic comprehension deficits. As patients become more demented and develop sensory aprosodia, they are at greater risk for disturbances in behavior and mood.

Semantic fluency performance of patients with cortical and subcortical neurodegenerative diseases.

Previous studies using the Animals Fluency Test have shown that dementia patients with Alzheimer's disease (AD), Huntington's disease (HD), or Parkinson's disease (PD) produce fewer correct words and have smaller semantic cluster sizes than controls or PD patients without dementia (PDND). Although the number of correct words generated by the patients with AD was positively correlated with mental status, cluster size, surprisingly, was not. To increase word output and increase the reliability of estimates of cluster size, semantic fluency was reexamined using the Supermarket Fluency Task. Overall, patients with HD or PD with dementia (PDD) exhibited reduced cluster sizes compared to older controls or PDND patients, but cluster sizes were only marginally reduced for patients with AD. These effects were evident only for female participants, because the cluster sizes for elderly control men were substantially smaller than those of elderly women. For the female patients with AD, cluster size was correlated with mental status, but the relationship was nonlinear. Cluster size was normal for mildly demented patients with AD, but much reduced for moderately or severely demented participants. In contrast to a previous report, in the present study the proportion of category labels generated was increased for patients with HD with dementia but not for patients with AD. This finding questions one line of evidence that semantic memory stores undergo "bottom-up" degradation in AD. Together with previous results, these findings indicate that semantic cluster size reflects efficiency of access to semantic knowledge which is similarly compromised in subcortical and cortical diseases.

[Plasma concentration of biochemical markers in pre-eclampsia-eclampsia and its association with the severity of the disease]. / Concentración plasmática de indicadores bioquímicos en la preeclampsia-eclampsia y su asociación con la severidad de la patología.

UNLABELLED: It has been demonstrated that the concentrations of molecules related to endothelial cell dysfunction, coagulation and vasoconstriction are altered in preeclamptic patients, but they have not been evaluated in their relationship with the severity of preeclampsia. OBJECTIVE: To determine the relationship between the plasmatic concentrations of fibronectin ED1+, antithrombin III, prostacyclin and thromboxane, and the severity of preeclampsia. METHODS: Peripheral blood was collected from 215 women in the third trimester of pregnancy, admitted to the Luis Castelazo Ayala Gynecology and Obstetrics Hospital with mild preeclampsia (n = 103), severe preeclampsia (n = 71), HELLP syndrome (n = 25) or eclampsia (n = 16). Plasma aliquots were stored at -70 degrees C until analysis. Fibronectin ED1+ was measured by ELISA; antithrombin III activity was determined using an automated amidolytic technique, and the concentrations of the stable metabolites 6-keto-prostagiandin F1a and thromboxane B2 were measured by RIA. Statistical analysis included ANOVA and logistic regression. RESULTS: Maternal age was similar in all participants. Prematurity and low birth weight were present in the patients with severe preeclampsia, HELLP and eclampsia. The values for fibronectin were similar among the 4 groups of patients. Antithrombin III activity was significantly lower in the patients with HELLP. In patients with severe preeclampsia and HELLP syndrome, prostacyclin (Pc) and thromboxane (Tbx) concentrations were significantly higher, and the Pc/Tbx ratio was lower than in patients with mild preeclampsia. Those patients who had the highest thromboxane levels and the lowest Pc/Tbx ratio had a higher chance to develop severe preeclampsia or HELLP (5 times), as well as to have premature babies (12 times) than patients with mild preeclampsia. CONCLUSIONS: Our study demonstrates relationships among antithrombin III activity, prostacyclin and thromboxane concentrations, and the severity of preeclampsia. These compounds were significantly more altered in patients with HELLP syndrome, probably due to a higher organic and vascular dysfunction. Plasma determination of these compounds may be valuable as a tool in the screening of preeclampsia, and as an indicator of severity of the disease.