Equivalence of the boson peak in glasses to the transverse acoustic van Hove singularity in crystals

We compare the atomic dynamics of the glass to that of the relevant crystal. In the spectra of inelastic scattering, the boson peak of the glass appears higher than the transverse acoustic (TA) singularity of the crystal. However, the density of states shows that they have the same number of states. Increasing pressure causes the transformation of the boson peak of the glass towards the TA singularity of the crystal. Once corrected for the difference in the elastic medium, the boson peak matches the TA singularity in energy and height. This suggests the identical nature of the two features.     

Dispersion Relation of an OH-Stretching Vibration from Inelastic X-Ray Scattering

We show that recent advances now allow us to measure the wave vector dependence of OH-stretching frequencies at energies around 400 meV by inelastic x-ray scattering using ID28@ESRF. We found a large, unexpected dispersion when we measured the dispersion relations of the hydrogen stretching frequencies of diaspore, alpha-AlOOH, where the hydrogen atoms participate in a hydrogen bond of intermediate strength. We can account for this behavior with density functional perturbation theory calculations and a simple model based on H-H interactions.     

Compositional effects on the structure and magnetotransport properties of lacunar La<Subscript>1-x</Subscript>MnO<Subscript>3-δ</Subscript> films (x>0) grown by MOCVD

Liquid-injection MOCVD was successfully applied to the growth of La_1-xMnO_3-films. A structural study by means of X-ray diffraction and transmission electron microscopy was performed on lanthanum manganite films grown under different (P[O₂]–T) conditions. The phase relations of lanthanum manganite with different manganese oxide phases (MnO, Mn₃O₄) are discussed, together with structural relations. Tuning of T_C via the concentration of La vacancies allows significant magnetoresistance at room temperature to be obtained (about 10% in a 1T field). PACS 68.55; 75.30; 81.15     

Electronic structure and phase separation in La<Subscript>x</Subscript>MnO<Subscript>3</Subscript> films (0.83≤<Emphasis Type="Italic">x</Emphasis>≤1.10): Optical and magnetooptical data

The variations in the electronic structure and the evolution of phase separation as a result of creation of vacancies or excess of lanthanum in lanthanum manganites are studied on the basis of analysis of optical and magnetic properties of La_xMnO₃ epitaxial films (0.83≤x≤1.10) in the fundamental absorption range. The Kerr effect, the temperature dependences of resistivity, optical density, and magnetoabsorption of light indicate the charge and magnetic phase separation in the films. The fine structure observed in the spectrum is attributed to spectral overlapping of electron transitions with charge transfer and geometrical resonances reflecting an inhomogeneous nanoscopic structure of the films, which strongly depends on stoichiometry and stresses emerging during film deposition. It is shown that, in contrast to bulk polycrystals, the gradient of stresses over the film thickness significantly affects the phase separation in the films.     

A study on microstructures and properties of P/M valve seats of hot forging by laser irradiation

A CO₂ laser was used as heating source for hot forging. Powder/metallurgy (P/M) valve seats for car engine was studied by this novel process. The effects of compression ratio and tempering temperature followed by laser irradiation on the microstructures and mechanical properties were investigated. It was indicated that the amount of the recrystallized grains increased with increasing compression ratio, especially when the compression ratio was above a certain value (18.70%), resulting in more refined grains. Good properties including density, radial crushing strength and hardness can be obtained by optimizing processing parameters.     

Isotope analyses of the lake sediments in the Plitvice Lakes,Croatia

The analyses of radioactive isotopes ¹⁴C, ¹³⁷Cs and ²¹⁰Pb, and stable isotope ¹³C were performed in the sediment cores, top 40 cm, taken in 2011 from karst lakes Pro??e and Kozjak in the Plitvice Lakes National Park, central Croatia. Frozen sediment cores were cut into 1 cm thick layers and dried. ¹⁴C activity in both carbonate and organic fractions was measured using accelerator mass spectrometry technique with graphite synthesis. ¹³⁷Cs, ²¹⁰Pb, ²¹⁴Pb and ²¹⁴Bi were measured by low level gamma spectrometry method on ORTECHPGe detector with the efficiency of 32%. Distribution of ¹⁴C activity from both lakes showed increase of the ¹⁴C activity in the top 10–12 cm in both carbonate and organic fractions as a response to thermonuclear bomb-produced ¹⁴C in the atmosphere in the sixties of the 20th century. Anthropogenically produced ¹³⁷Cs was also observed in sediment profiles. Sedimentation rates for both lake sediments were estimated based on the unsupported ²¹⁰Pb activity. Different ¹⁴C activity of the carbonate fraction (63–80 pMC, percent of modern carbon) and organic fraction (82–93 pMC) is the result of geochemical and biological processes of the sediment precipitation in the lake waters. This is also confirmed by the δ ¹³ C values of both fractions. Carbon isotope composition, a ¹⁴ C and δ ¹³ C, was compared with the lake sediments from the same lakes collected in 1989 and 2003.     

Sporulenes, heptaprenyl metabolites from Bacillus subtilis spores

Sporulene, a C 35-terpenoid hydrocarbon with an unusual pentacyclic structure, is produced by Bacillus subtilis during sporulation.     

Development and validation of a sensitive and fast solid-phase spectrophotometric procedure for phenol determination in pharmaceuticals

A very sensitive, simple, and fast solid-phase spectrophotometric procedure for the determination of phenol using the p-nitrobenzenediazonium reagent (DAR reagent) was developed. This procedure is based on the simultaneous concentration of the orange product on a Dowex 1-X2 anion exchanger within 15 min, and a direct absorbance measurement of the sorbed species at both 530 nm (the absorption maximum of the phenol-DAR in the resin phase) and 700 nm (the range where only the resin absorbs light). Quality control and evaluation of the analytical parameters was carried out using a comprehensive prevalidation strategy. The linearity of the method was confirmed within an analyte working range from 0.01 to 0.10 μmol (0.2 to 2.0 nmol mL(-1)). The precision ranged from ±1.17 to ±9.61%; the accuracy ranged from -17.50 to +17.81%. The evaluated limiting values were L(D) = 0.0013 μmol and L(Q) = 0.0082 μmol. The DAR-SPS method was successfully applied to the determination of phenol in a pharmaceutical sample of salicylic acid (98.0-100.0%) and vaccines (98.0-103.4%).