3,171 research outputs found
Apparatus for purging systems handling toxic, corrosive, noxious and other fluids Patent
Fluid transferring system design for purging toxic, corrosive, or noxious fluids and fumes from materials handling equipment for cleansing and accident preventio
Colorado v. Connelly: The Demise of Free Will as an Independent Basis for Finding a Confession Involuntary
Soft Mode Dynamics Above and Below the Burns Temperature in the Relaxor Pb(Mg_1/3Nb_2/3)O_3
We report neutron inelastic scattering measurements of the lowest-energy
transverse optic (TO) phonon branch in the relaxor Pb(Mg_1/3Nb_2/3)O_3 from 400
to 1100 K. Far above the Burns temperature T_d ~ 620 K we observe well-defined
propagating TO modes at all wave vectors q, and a zone center TO mode that
softens in a manner consistent with that of a ferroelectric soft mode. Below
T_d the zone center TO mode is overdamped. This damping extends up to, but not
above, the waterfall wave vector q_wf, which is a measure of the average size
of the PNR.Comment: 4 pages, 4 figures; modified discussion of Fig. 3, shortened
captions, added reference, corrected typos, accepted by Phys. Rev. Let
Dynamical effects of the nanometer-sized polarized domains in Pb(Zn1/3Nb2/3)O3
Recent neutron scattering measurements performed on the relaxor ferroelectric
Pb[(Zn1/3Nb2/3)0.92Ti0.08]O3 (PZN-8%PT) in its cubic phase at 500 K, have
revealed an anomalous ridge of inelastic scattering centered ~0.2 A-1 from the
zone center (Gehring et al., Phys. Rev. Lett. 84, 5216 (2000)). This ridge of
scattering resembles a waterfall when plotted as a phonon dispersion diagram,
and extends vertically from the transverse acoustic (TA) branch near 4 meV to
the transverse optic (TO) branch near 9 meV. No zone center optic mode was
found. We report new results from an extensive neutron scattering study of pure
PZN that exhibits the same waterfall feature. We are able to model the dynamics
of the waterfall using a simple coupled-mode model that assumes a strongly
q-dependent optic mode linewidth Gamma1(q) that increases sharply near 0.2 A-1
as one approaches the zone center. This model was motivated by the results of
Burns and Dacol in 1983, who observed the formation of a randomly-oriented
local polarization in PZN at temperatures far above its ferroelectric phase
transition temperature. The dramatic increase in Gamma1 is believed to occur
when the wavelength of the optic mode becomes comparable to the size of the
small polarized micro-regions (PMR) associated with this randomly-oriented
local polarization, with the consequence that longer wavelength optic modes
cannot propagate and become overdamped. Below Tc=410 K, the intensity of the
waterfall diminishes. At lowest temperatures ~30 K the waterfall is absent, and
we observe the recovery of a zone center transverse optic mode near 10.5 meV.Comment: 8 pages, 9 figures (one color). Submitted to Physical Review
Limits to Plasticity in Gray Wolf, Canis lupus, Pack Structure: Conservation Implications for Recovering Populations
We documented the dynamics of the Five Corners Pack (FCP) in east-central Minnesota and northwestern Wisconsin through the loss and replacement of four alpha-females over a four-year period. This pack remained intact and produced offspring during the period despite the annual loss of the alpha female. However, we observed a disintegration of the pack after four consecutive alpha females died, at least two of which were due to illegal killing by humans. Our observations generally support the hypothesis that “single-parent” wolf packs may be more prevalent in areas with low densities of wolves and high densities of ungulate prey. Our observations also highlight the need to assess the potential negative impacts of wolf removal on pack structure and persistence at local and regional scales
Coexistence and competition of local- and long-range polar orders in a ferroelectric relaxor
We have performed a series of neutron diffuse scattering measurements on a
single crystal of the solid solution Pb(ZnNb)O (PZN) doped
with 8% PbTiO (PT), a relaxor compound with a Curie temperature T K, in an effort to study the change in local polar orders from the polar
nanoregions (PNR) when the material enters the ferroelectric phase. The diffuse
scattering intensity increases monotonically upon cooling in zero field, while
the rate of increase varies dramatically around different Bragg peaks. These
results can be explained by assuming that corresponding changes occur in the
ratio of the optic and acoustic components of the atomic displacements within
the PNR. Cooling in the presence of a modest electric field oriented
along the [111] direction alters the shape of diffuse scattering in reciprocal
space, but does not eliminate the scattering as would be expected in the case
of a classic ferroelectric material. This suggests that a field-induced
redistribution of the PNR has taken place
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