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.

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.

Environmental Exposure-Associated Human Health Risk of Dioxin Compounds in the Vicinity of a Municipal Solid Waste Incinerator in Shanghai, China.

In order to assess environmental exposure-associated human health risk of dioxin compounds for the population in the vicinity of a municipal solid waste incinerator (MSWI) in Shanghai, the atmospheric samples (n = 24) and soils samples (n = 96) were collected and analyzed to obtain the concentration level, pollution characteristics and seasonal changes of dioxin compounds in environmental medias. The toxicity equivalent concentration range of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) was 30.9-409 fg WHO-TEQ·m-3 in atmosphere and 0.362-8.55 ng WHO-TEQ·kg-1 in soil. The non-carcinogenic health risk and carcinogenic health risk from PCDD/Fs environmental exposure of people living in the vicinity of the MSWI in Shanghai were all within the allowable range of the US Environmental Protection Agency, which implied that the MSWI in Shanghai did not produce additional risk for the population living in its vicinity.

[A concentration-response observation of hydromorphone combined with ropivacaine in labor analgesia].

Objective: To investigate the median effective dose (ED(50)) of hydromorphone and the appropriate concentration of ropivacaine combined with hydromorphone in epidural labor analgesia. Methods: One hundred and forty nulliparous women undergoing labor selected for delivery with epidural analgesia were enrolled in our hospital from January to June 2016. The first of top 50 women received 0.12% ropivacaine plus 20 µg/ml hydromorphone complex solution, then sequential women were used the modified sequential method to determine the ED(50) and ED(95) of hydromorphone. The other 90 women were randomly divided and receieved 0.08% ropivacaine and 15 µg/ml hydromorphone(H1 group), 0.10% ropivacaine and 15 µg/ml hydromorphone (H2 group), 0.12% ropivacaine and 15 µg/ml hydromorphone (group H3) respectively for epidural labor analgesia. In the course of labor, block levels of epidural analgesia, the Bromage scores, analgesia scores and fetal heart rate-uterine concraction were monitored. In addition, onset time of anesthesia, labor time, mode of delivery, cases of increased oxytocin using, neonatal Apgar score, incidence of nausea and vomiting, itching and fetal heart reduction were recorded. Results: The ED(50) and ED(95) values of hydromorphone were 10.49 (95% CI: 8.89-11.79) and 15.15 (95% CI: 13.25-22.25) µg/ml respectively. The onset time in group H1 was significantly longer than those in group H2 and H3((14.23±3.82) , ( 11.32±2.16), (10.83±2.56)min, respectively), the difference was statistically significant (t=5.854, 6.212, all P<0.05). Analgesic VAS score at 30, 60 and 90 min time points in H1 group was significantly higher than that in H2 group and H3 group (all P<0.05). VAS score at withdrawal in H1 group was significantly higher than that in group H3 ( (3.25±0.75) vs (0.27±0.12) ), the difference was statistically significant ( t=9.314, P<0.05). VAS scores at the fourth, fifth, sixth contractions after analgesia in H1 group were significantly higher than those in H2 and H3 groups (all P<0.05). The incidence of motor nerve block in group H3 was higher than that in group H1 and group H2 (26.67%, 6.66%, 3.33%, respectively), the difference was statistically significant (χ(2)=6.413, 4.320, all P<0.05). Conclusions: 0.10% ropivacaine combined with 15 µg/ml hydromorphone has a good analgesic effect, slight motor block, high safety and worthy clinical application for labor analgesia.

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.

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 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.

Pressure induced second-order structural transition in Sr3Ir2O7.

We conducted in situ angle dispersive high pressure x-ray diffraction experiments on Sr3Ir2O7 up to 23.1 GPa at 25 K with neon as the pressure transmitting medium. Pressure induces a highly anisotropic compressional behavior seen where the tetragonal plane is compressed much faster than the perpendicular direction. By analyzing different aspects of the diffraction data, a second-order structural transition is observed at approximately 14 GPa, which is accompanied by the insulating state to nearly metallic state at 13.2 GPa observed previously (Li et al 2013 Phys. Rev. B 87 235127). Our results highlight the coupling between electronic state and lattice structure in Sr3Ir2O7 under pressure.

Persistence of Jahn-Teller distortion up to the insulator to metal transition in LaMnO3.

High pressure, low temperature Raman measurements performed on LaMnO3 up to 34 GPa provide the first experimental evidence for the persistence of the Jahn-Teller distortion over the entire stability range of the insulating phase. This result resolves the ongoing debate about the nature of the pressure driven insulator to metal transition (IMT), demonstrating that LaMnO3 is not a classical Mott insulator. The formation of domains of distorted and regular octahedra, observed from 3 to 34 GPa, sheds new light on the mechanism behind the IMT suggesting that LaMnO3 becomes metallic when the fraction of undistorted octahedra domains increases beyond a critical threshold.

[Analytical studies on calcium and microelements in calcined longgu (an animal bone)].

The main constituent (CaCO3) and microelements of Longgu (an animal bone) have been analysed qualitatively and quantitatively by orthogonal design. The result shows that the optimum conditions for calcining Longgu are: temperature--750 degrees C, time--4'30'', size of the bone--8.5g.