Doming Modes and Dynamics of Model Heme Compounds

Synchrotron far-IR spectroscopy and density-functional calculations are used to characterize the low-frequency dynamics of model heme FeCO compounds. The “doming” vibrational mode in which the iron atom moves out of the porphyrin plane while the periphery of this ring moves in the opposite direction determines the reactivity of oxygen with this type of molecule in biological systems. Calculations of frequencies and absorption intensities and the measured pressure dependence of vibrational modes in the model compounds are used to identify the doming and related normal modes

Structure and Properties of Dense Silica Glass

The O K-edge x-ray Raman scattering (XRS), Brillouin scattering and diffraction studies on silica glass at high pressure have been elucidated in a unified manner using model structures obtained from First-Principles molecular dynamics calculations. This study provides a comprehensive understanding on how the structure is related to the physical and electronic properties. The origin of the "two peak" pattern in the XRS is found to be the result of increased packing of oxygen near the Si and is not a specific sign for sixfold coordination. The compression mechanism involving the presence of 5- and 6-fold coordinated silicon is confirmed. A slight increase in the silicon-oxygen coordination higher than six was found to accompany the increase in the acoustic wave velocity near 140 GPa

The electrical conductivity of Al2O3 under shock-compression

Sapphire (Al2O3) crystals are used below 100 GPa as anvils and windows in dynamic-compression experiments because of their transparency and high density. Above 100 GPa shock pressures, sapphire becomes opaque and electrically conducting because of shock-induced defects. Such effects prevent temperature and dc conductivity measurements of materials compressed quasi-isentropically. Opacities and electrical conductivities at ~100 GPa are non-equilibrium, rather than thermodynamic parameters. We have performed electronic structure calculations as a guide in predicting and interpreting shock experiments and possibly to discover a window up to ~200 GPa. Our calculations indicate shocked sapphire does not metallize by band overlap at ~300 GPa, as suggested previously by measured non-equilibrium data. Shock-compressed Al2O3 melts to a metallic liquid at ~500 GPa and 10,000 K and its conductivity increases rapidly to ~2000 Ω−1cm−1 at ~900 GPa. At these high shock temperatures and pressures sapphire is in thermal equilibrium. Calculated conductivity of Al2O3 is similar to those measured for metallic fluid H, N, O, Rb, and Cs. Despite different materials, pressures and temperatures, and compression techniques, both experimental and theoretical, conductivities of all these poor metals reach a common end state typical of strong-scattering disordered materials

Atomically dispersed quintuple nitrogen and oxygen co-coordinated zirconium on graphene-type substrate for highly efficient oxygen reduction reaction.

A cost-effective and long stability catalyst with decent electrochemical activity would play a crucial role in accelerating applications of metal-air batteries. Here, we report quintuple nitrogen and oxygen co-coordinated Zr sites on graphene (Zr-N/O-C) by using a ball-milling, solid-solution-assisted pyrolysis method. The as-prepared Zr-N/O-C catalyst with 2.93 wt % Zr shows a half-wave potential of 0.910 V, an onset potential of 1.000 V in 0.1 M KOH, impressive durability (95.1% remains after 16,000 s), and long-term stability (5 mV loss over 10,000 cycles). Zn-air batteries with the Zr-N/O-C electrode exhibit a maximum power density of 217.9 mW cm−2 and a high cycling life of over 1,000 h, exceeding the counterpart equipped with a Pt/C benchmark. Theoretical simulations demonstrate that nitrogen and oxygen dual-ligand confinement effectively tunes the d-band center and balances key intermediates binding energy of intrinsic quintuple coordination Zr sites

Does sex education before college protect students from sexual assault in college?

Purpose College-bound young people experience sexual assault, both before and after they enter college. This study examines historical risk factors (experiences and exposures that occurred prior to college) for penetrative sexual assault (PSA) victimization since entering college. Methods A cross-sectional study, including an online population-based quantitiative survey with undergraduate students was conducted in spring 2016. Bivariate analyses and multivariable regressions examined risk and protective factors associated with ever experiencing PSA since entering college. Concurrently-collected in-depth ethnographic interviews with 151 students were reviewed for information related to factors identified in the survey. Results In bivariate analyses, multiple historical factors were significantly associated with PSA in college including adverse childhood experiences and having experienced unwanted sexual contact before college (for women) and initiation of alcohol, marijuana, and sexual behaviors before age 18. Significant independent risk factors for college PSA included female gender, experiencing unwanted sexual contact before college, first oral sex before age 18, and “hooking up” (e.g., causual sex or sex outside a committed partnership) in high school. Receipt of school-based sex education promoting refusal skills before age 18 was an independent protective factor; abstinence-only instruction was not. In the ethnographic interviews, students reported variable experiences with sex education before college; many reported it was awkward and poorly delivered. Conclusions Multiple experiences and exposures prior to college influenced the risk of penetrative sexual assault in college. Pre-college comprehensive sexuality education, including skills-based training in refusing unwanted sex, may be an effective strategy for preventing sexual assault in college. Sexual assault prevention needs to begin earlier; successful prevention before college should complement prevention efforts once students enter college