The high-pressure behavior of CaMoO4

We report a high-pressure study of tetragonal scheelite-type CaMoO4 up to 29 GPa. In order to characterize its high-pressure behavior, we have combined Raman and optical-absorption measurements with density-functional theory calculations. We have found evidence of a pressure-induced phase transition near 15 GPa. Experiments and calculations agree in assigning the high-pressure phase to a monoclinic fergusonite-type structure. The reported results are consistent with previous powder x-ray-diffraction experiments, but are in contradiction with the conclusions obtained from earlier Raman measurements, which support the existence of more than one phase transition in the pressure range covered by our studies. The observed scheelite-fergusonite transition induces significant changes in the electronic band gap and phonon spectrum of CaMoO4. We have determined the pressure evolution of the band gap for the low- and high-pressure phases as well as the frequencies and pressure dependences of the Raman-active and infrared-active modes. In addition, based upon calculations of the phonon dispersion of the scheelite phase, carried out at a pressure higher than the transition pressure, we propose a possible mechanism for the reported phase transition. Furthermore, from the calculations we determined the pressure dependence of the unit-cell parameters and atomic positions of the different phases and their room-temperature equations of state. These results are compared with previous experiments showing a very good agreement. Finally, information on bond compressibility is reported and correlated with the macroscopic compressibility of CaMoO4. The reported results are of interest for the many technological applications of this oxide.Comment: 36 pages, 10 figures, 8 table

Mixed-Mode Electro-Optical Operation of Ge2Sb2Te5 Nanoscale Crossbar Devices

This is the author accepted manuscript. The final version is freely available from Wiley via the DOI in this record.The use of phase-change materials for a range of exciting new optoelectronic applications from artificial retinas to ultrahigh-resolution displays requires a thorough understanding of how these materials perform under a combination of optical and electrical stimuli. This study reports for the first time the complex link between the electronic and optical properties in real-world crossbar nanoscale devices constructed by confining a thin layer of Ge2Sb2Te5 between transparent indium tin oxide electrodes, forming an optical nanocavity. A novel proof-of-concept device that can be operated by a combination of optical and electrical stimuli is presented, leading the way for the development of further applications based on mixed-mode electro-optical operation.CONACYT. Grant Number: 215365. EPSRC. Grant Numbers: EP/J018783/1, EP/M015173/1, EP/M015130/1, EP/J018694/

Physicochemical, traction and tribofilm formation properties of three octanoate-, laurate- and palmitate-anion based ionic liquids

Three new ionic liquids with different anions and the same cation were synthesized from fatty acids through a metathesis reaction.All the ionic liquidswere identified viaNMRand FTIR and several properties (density, viscosity, thermal, and environmental) were measured. Traction tests were performed under different entrainment speeds (10–2000 mm/s), at slide-roll ratio (SRR) of 50% and 30 N-load, and at different temperatures (40, 60, 80 and 100 °C) using a mini-traction machine (MTM). Tribofilm formation tests were also made in the MTM at 50 N-load, 150 mm/s of entrainment speed, at SRR of 50% and temperature of 100 °C, for 60 min. This work showed that the alkyl chain length in the anion affects properties such as viscosity, toxicity, biodegradability and lubrication. Viscosity decreased with increasing alkyl chain length but only below 60 °C, at higher temperatures the viscosity values of the ionic liquids converge. The toxicity increases with the alkyl chain length; whereas, biodegradability shows the opposite behavior. These novel ionic liquids are much better from both toxicity and biodegradability points of view than the [N8881][TFSI] ionic liquid, which contains the same cation and anion not coming from fatty acids. The ionic liquids at low temperature (40 °C) performed under elastohydrodynamic lubrication and changed to mixed lubrication at higher temperatures and decreasing speeds, according to the alkyl chain length of each anion. All ionic liquids adsorbed on the steel surfaces, and the tribofilm thickness and the kinetics of formation were different

Nanomechanics of graphene oxide-bacteriophage based self-assembled porous composites.

Graphene oxide, integrated with the filamentous bacteriophage M13, forms a 3D large-scale multifunctional porous structure by self-assembly, with considerable potential for applications. We performed Raman spectroscopy under pressure on this porous composite to understand its fundamental mechanics. The results show that at low applied pressure, the [Formula: see text] bonds of graphene oxide stiffen very little with increasing pressure, suggesting a complicated behaviour of water intercalated between the graphene layers. The key message of this paper is that water in a confined space can have a significant impact on the nanostructure that hosts it. We introduced carbon nanotubes during the self-assembly of graphene oxide and M13, and a similar porous macro-structure was observed. However, in the presence of carbon nanotubes, pressure is transmitted to the [Formula: see text] bonds of graphene oxide straightforwardly as in graphite. The electrical conductivity of the composite containing carbon nanotubes is improved by about 30 times at a bias voltage of 10 V. This observation suggests that the porous structure has potential in applications where good electrical conductivity is desired, such as sensors and batteries

The electronic structure of zircon-type orthovanadates: Effects of high-pressure and cation substitution

The electronic structure of four ternary-metal oxides containing isolated vanadate ions is studied. Zircon-type YVO4, YbVO4, LuVO4, and NdVO4 are investigated by high-pressure optical-absorption measurements up to 20 GPa. First-principles calculations based on density-functional theory were also performed to analyze the electronic band structure as a function of pressure. The electronic structure near the Fermi level originates largely from molecular orbitals of the vanadate ion, but cation substitution influence these electronic states. The studied ortovanadates, with the exception of NdVO4, undergo a zircon-scheelite structural phase transition that causes a collapse of the band-gap energy. The pressure coefficient dEg/dP show positive values for the zircon phase and negative values for the scheelite phase. NdVO4 undergoes a zircon-monazite-scheelite structural sequence with two associated band-gap collapses.Comment: 35 pages, 11 figures, 2 Tables, 52 reference

Rubidium-Rich Asymptotic Giant Branch Stars

A long debated issue concerning the nucleosynthesis of neutron-rich elements in Asymptotic Giant Branch (AGB) stars is the identification of the neutron source. We report intermediate-mass (4 to 8 solar masses) AGB stars in our Galaxy that are rubidium-rich owing to overproduction of the long-lived radioactive isotope 87Rb, as predicted theoretically 40 years ago. This represents a direct observational evidence that the 22Ne(alpha,n)25Mg reaction must be the dominant neutron source in these stars. These stars then challenge our understanding of the late stages of the evolution of intermediate-mass stars and would promote a highly variable Rb/Sr environment in the early solar nebula

Proper motions of the HH1 jet

We describe a new method for determining proper motions of extended objects, and a pipeline developed for the application of this method. We then apply this method to an analysis of four epochs of [S~II] HST images of the HH~1 jet (covering a period of $\sim 20$~yr). We determine the proper motions of the knots along the jet, and make a reconstruction of the past ejection velocity time-variability (assuming ballistic knot motions). This reconstruction shows an "acceleration" of the ejection velocities of the jet knots, with higher velocities at more recent times. This acceleration will result in an eventual merging of the knots in $\sim 450$~yr and at a distance of $\sim 80"$ from the outflow source, close to the present-day position of HH~1.Comment: 12 pages, 8 figure

Use of Non-Steroidal Anti-Inflammatory Drugs That Elevate Cardiovascular Risk: An Examination of Sales and Essential Medicines Lists in Low-, Middle-, and High-Income Countries

PMCID: PMC3570554This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited