514 research outputs found
Vibrational density of states of silicon nanoparticles
The vibrational density of states of silicon nanoparticles in the range from
2.3 to 10.3 nm is studied with the help of molecular-dynamics simulations. From
these simulations the vibrational density of states and frequencies of
bulk-like vibrational modes at high-symmetry points of the Brillouin-zone have
been derived. The results show an increase of the density of states at low
frequencies and a transfer of modes from the high-frequency end of the spectrum
to the intermediate range. At the same time the peak of transverse optical
modes is shifted to higher frequencies. These observations are in line with
previous simulation studies of metallic nanoparticles and they provide an
explanation for a previously observed discrepancy between experimental and
theoretical data [C. Meier et al., Physica E, 32, 155 (2006)].Comment: 7 pages, 5 figure; accepted for publication in Phys. Rev.
Origin of Low Thermal Conductivity in Nuclear Fuels
Using a novel many-body approach, we report lattice dynamical properties of
UO2 and PuO2 and uncover various contributions to their thermal conductivities.
Via calculated Grueneisen constants, we show that only longitudinal acoustic
modes having large phonon group velocities are efficient heat carriers. Despite
the fact that some optical modes also show their velocities which are extremely
large, they do not participate in the heat transfer due to their unusual
anharmonicity. Ways to improve thermal conductivity in these materials are
discussed.Comment: 4 pages, 3 figures, 1 tabl
Estimates of Soil Solution Ionic Strength and the Determination of pH in West Australian Soils
The average ionic strength of 20 West Australian soils was found to be 0.0048. The effects of three electrolytes (deionized water, CaCl2 and KNO3), three ionic strengths (0.03, 0.005 and soil ionic strength at field capacity, Is) and two soil liquid ratios (1:5 and 1:10) on the pH of 15 soils were investigated. pH measurements in solutions of ionic strength 0.005 differed the least from measurements made at Is. The differences that occurred in comparisons with distilled water or CaCl2 of ionic strength 0.03 (0.01 M) were much greater (≥0.4 pH units). An extractant with an ionic strength of 0.005 may provide a more realistic measure of pH in the field than distilled water or 0.01 M CaCl2 for West Australian soils
Lorentz covariance of the canonical perfect lens
The canonical perfect lens--comprising three slabs, each made of a linear,
homogeneous, bianisotropic material with orthorhombic symmetry--is Lorentz
covariant
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