The effect of manganese oxide on the sinterability of hydroxyapatite

The sinterability of manganese oxide (MnO2) doped hydroxyapatite (HA) ranging from 0.05 to 1 wt% was investigated. Green samples were prepared and sintered in air at temperatures ranging from 1000 to 1400 °C. Sintered bodies were characterized to determine the phase stability, grain size, bulk density, hardness, fracture toughness and Young's modulus. XRD analysis revealed that the HA phase stability was not disrupted throughout the sintering regime employed. In general, samples containing less than 0.5 wt% MnO2 and when sintered at lower temperatures exhibited higher mechanical properties than the undoped HA. The study revealed that all the MnO2-doped HA achieved >99% relative density when sintered at 1100–1250 °C as compared to the undoped HA which could only attained highest value of 98.9% at 1150 °C. The addition of 0.05 wt% MnO2 was found to be most beneficial as the samples exhibited the highest hardness of 7.58 GPa and fracture toughness of 1.65 MPam1/2 as compared to 5.72 GPa and 1.22 MPam1/2 for the undoped HA when sintered at 1000 °C. Additionally, it was found that the MnO2-doped samples attained E values above 110 GPa when sintered at temperature as low as 1000 °C if compared to 1050 °C for the undoped HA

In vitro assessment of the toxicity of lead (Pb2+) to phycocyanin

© 2017 Elsevier Ltd This work reports the influence of lead (Pb2+) on fluorescence characteristics and protein structure of phycocyanin molecules experimentally in vitro. The fluorescence intensity decreases with the increasing concentration of Pb2+ from 0 to 5 × 10−5 mol L−1, showing the fluorescence quenching of phycocyanin by Pb2+. The quenching process is suggested to be static regarding the calculation results and the experimental results of time-resolved fluorescence decay profiles. The synchronous fluorescence spectra show that the effect of Pb2+ on the Tyr residues of phycocyanin is more significant than the Trp residues. The forming of aggregation by the interaction of Pb2+ with phycocyanin molecules is suggested from the results of resonance light scattering spectra. The UV–Vis spectra of the protein skeleton of phycocyanin have a red-shift of about 10 nm with increasing the Pb2+ concentration from 0 to 5 × 10−5 mol L−1, indicating a change in the protein skeleton and its secondary structure. With the increasing Pb2+ concentration, the two negative peaks (209 nm and 218 nm) on circular dichroism spectra become smaller, showing a decrease of the α-helix structure. These results may give people a deeper understanding of that how the heavy metal (Pb2+) can affect the chemo-physical properties of phycocyanin

Penning trap and vacuum noise

A number of comments are provided on Rogers's model experiment to measure the circular Unruh vacuum noise by means of a hyperbolic Penning trap inside a microwave cavity. It is suggested that cylindrical Penning traps, being geometrically simpler, and controlled almost at the same level of accuracy as the hyperbolic trap, might be a better choice for such an experiment. Besides, the microwave modes of the trap itself, of known analytical structure, can be directly used in trying to obtain measurable results for such a tiny noise effect.Comment: 7 LaTex pages, published text and references with title

Spin Susceptibility of a 2D Electron System in GaAs towards the Weak Interaction Region

We determine the spin susceptibility $\chi$ in the weak interaction regime of a tunable, high quality, two-dimensional electron system in a GaAs/AlGaAs heterostructure. The band structure effects, modifying mass and g-factor, are carefully taken into accounts since they become appreciable for the large electron densities of the weak interaction regime. When properly normalized, $\chi$ decreases monotonically from 3 to 1.1 with increasing density over our experimental range from 0.1 to $4\times10^{11} cm^{-2}$. In the high density limit, $\chi$ tends correctly towards $\chi\to 1$ and compare well with recent theory.Comment: Submitted to Physical Review