1,112 research outputs found
Effect of sarcoptic mange treatment on growth performance of pigs
Growth performance of 135 sarcoptic mange mite-infested pigs (8 pens of 15-20 pigs each) was evaluated for an 8-week period during June-August, 1985. Pigs in 6 pens were treated with the acaricide TAKTIC EC, whereas two pens were maintained as nontreated controls. Results indicated that although treatment for sarcoptic mange was effective, it did not improve average daily gains in TAKTIC EC-treated pigs.; Swine Day, Manhattan, KS, November 20, 198
Electrodynamics near the Metal-to-Insulator Transition in V3O5
The electrodynamics near the metal-to-insulator transitions (MIT) induced, in
V3O5 single crystals, by both temperature (T) and pressure (P) has been studied
by infrared spectroscopy. The T- and P-dependence of the optical conductivity
may be explained within a polaronic scenario. The insulating phase at ambient T
and P corresponds to strongly localized small polarons. Meanwhile the T-induced
metallic phase at ambient pressure is related to a liquid of polarons showing
incoherent dc transport, in the P-induced metallic phase at room T strongly
localized polarons coexist with partially delocalized ones. The electronic
spectral weight is almost recovered, in both the T and P induced metallization
processes, on an energy scale of 1 eV, thus supporting the key-role of
electron-lattice interaction in the V3O5 metal-to-insulator transition.Comment: 7 pages, 5 figure
Pressure-tuning of the c-f hybridization in Yb metal detected by infrared spectroscopy up to 18 GPa
It has been known that the elemental Yb, a divalent metal at mbient pressure,
becomes a mixed-valent metal under external pressure, with its valence reaching
~2.6 at 30 GPa. In this work, infrared spectroscopy has been used to probe the
evolution of microscopic electronic states associated with the valence
crossover in Yb at external pressures up to 18 GPa. The measured infrared
reflectivity spectrum R(w) of Yb has shown large variations with pressure. In
particular, R(w) develops a deep minimum in the mid-infrared, which shifts to
lower energy with increasing pressure. The dip is attributed to optical
absorption due to a conduction c-f electron hybridization state, similarly to
those previously observed for heavy fermion compounds. The red shift of the dip
indicates that the - hybridization decreases with pressure, which is
consistent with the increase of valence.Comment: 2 pages, to appear in J. Phys. Soc. Jpn. Supp
Optical evidence for a spin-filter effect in the charge transport of
We have measured the optical reflectivity of
as a function of temperature between 1.5 and 300
and in external magnetic fields up to 7 . The slope at the onset of the
plasma edge feature in increases with decreasing temperature and
increasing field but the plasma edge itself does not exhibit the remarkable
blue shift that is observed in the binary compound . The analysis of
the magnetic field dependence of the low temperature optical conductivity
spectrum confirms the previously observed exponential decrease of the
electrical resistivity upon increasing, field-induced bulk magnetization at
constant temperature. In addition, the individual exponential magnetization
dependences of the plasma frequency and scattering rate are extracted from the
optical data.Comment: submitted to Phys. Rev. Let
Magneto-optical evidence of double exchange in a percolating lattice
Substituting by in ferromagnetic leads to a percolation
limited magnetic ordering. We present and discuss magneto-optical data of the
series, based on measurements of the reflectivity
from the far infrared up to the ultraviolet, as a function of
temperature and magnetic field. Via the Kramers-Kronig transformation of
we extract the complete absorption spectra of samples with
different values of . The change of the spectral weight in the Drude
component by increasing the magnetic field agrees with a scenario based on the
double exchange model, and suggests a crossover from a ferromagnetic metal to a
ferromagnetic Anderson insulator upon increasing -content at low
temperatures.Comment: 10 pages, 3 figure
Topology of amorphous tetrahedral semiconductors on intermediate lengthscales
Using the recently-proposed ``activation-relaxation technique'' for
optimizing complex structures, we develop a structural model appropriate to
a-GaAs which is almost free of odd-membered rings, i.e., wrong bonds, and
possesses an almost perfect coordination of four. The model is found to be
superior to structures obtained from much more computer-intensive tight-binding
or quantum molecular-dynamics simulations. For the elemental system a-Si, where
wrong bonds do not exist, the cost in elastic energy for removing odd-membered
rings is such that the traditional continuous-random network is appropriate.
Our study thus provides, for the first time, direct information on the nature
of intermediate-range topology in amorphous tetrahedral semiconductors.Comment: 4 pages, Latex and 2 postscript figure
Infrared phonon dynamics of multiferroic BiFeO3 single crystal
We discuss the first infrared reflectivity measurement on a BiFeO3 single
crystal between 5 K and room temperature. The 9 predicted ab-plane E phonon
modes are fully and unambiguously determined. The frequencies of the 4 A1
c-axis phonons are found. These results settle issues between theory and data
on ceramics. Our findings show that the softening of the lowest frequency E
mode is responsible for the temperature dependence of the dielectric constant,
indicating that the ferroelectric transition in BiFeO3 is soft-mode driven.Comment: 5 pages (figures included
Pressure dependence of the charge-density-wave gap in rare-earth tri-tellurides
We investigate the pressure dependence of the optical properties of CeTe,
which exhibits an incommensurate charge-density-wave (CDW) state already at 300
K. Our data are collected in the mid-infrared spectral range at room
temperature and at pressures between 0 and 9 GPa. The energy for the single
particle excitation across the CDW gap decreases upon increasing the applied
pressure, similarly to the chemical pressure by rare-earth substitution. The
broadening of the bands upon lattice compression removes the perfect nesting
condition of the Fermi surface and therefore diminishes the impact of the CDW
transition on the electronic properties of Te.Comment: 5 pages, 4 figure
Optical properties of the Ce and La di-telluride charge density wave compounds
The La and Ce di-tellurides LaTe and CeTe are deep in the
charge-density-wave (CDW) ground state even at 300 K. We have collected their
electrodynamic response over a broad spectral range from the far infrared up to
the ultraviolet. We establish the energy scale of the single particle
excitation across the CDW gap. Moreover, we find that the CDW collective state
gaps a very large portion of the Fermi surface. Similarly to the related rare
earth tri-tellurides, we envisage that interactions and Umklapp processes play
a role in the onset of the CDW broken symmetry ground state
Chemical pressure and hidden one-dimensional behavior in rare earth tri-telluride charge density wave compounds
We report on the first optical measurements of the rare-earth tri-telluride
charge-density-wave systems. Our data, collected over an extremely broad
spectral range, allow us to observe both the Drude component and the
single-particle peak, ascribed to the contributions due to the free charge
carriers and to the charge-density-wave gap excitation, respectively. The data
analysis displays a diminishing impact of the charge-density-wave condensate on
the electronic properties with decreasing lattice constant across the
rare-earth series. We propose a possible mechanism describing this behavior and
we suggest the presence of a one-dimensional character in these two-dimensional
compounds. We also envisage that interactions and umklapp processes might play
a relevant role in the formation of the charge-density-wave state in these
compounds.Comment: 8 pages, 5 figure
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