85 research outputs found
Infrared and THz studies of polar phonons and improper magnetodielectric effect in multiferroic BFO3 ceramics
BFO3 ceramics were investigated by means of infrared reflectivity and time
domain THz transmission spectroscopy at temperatures 20 - 950 K, and the
magnetodielectric effect was studied at 10 - 300 K, with the magnetic field up
to 9 T. Below 175 K, the sum of polar phonon contributions into the
permittivity corresponds to the value of measured permittivity below 1 MHz. At
higher temperatures, a giant low-frequency permittivity was observed, obviously
due to the enhanced conductivity and possible Maxwell-Wagner contribution.
Above 200 K the observed magnetodielectric effect is caused essentially through
the combination of magnetoresistance and the Maxwell-Wagner effect, as recently
predicted by Catalan (Appl. Phys. Lett. 88, 102902 (2006)). Since the
magnetodielectric effect does not occur due to a coupling of polarization and
magnetization as expected in magnetoferroelectrics, we call it improper
magnetodielectric effect. Below 175 K the magnetodielectric effect is by
several orders of magnitude lower due to the decreased conductivity. Several
phonons exhibit gradual softening with increasing temperature, which explains
the previously observed high-frequency permittivity increase on heating. The
observed non-complete phonon softening seems to be the consequence of the
first-order nature of the ferroelectric transition.Comment: subm. to PRB. revised version according to referees' report
Origin of magnetoelectric behavior in BiFeO
The magnetoelectric behavior of BiFeO has been explored on the basis of
accurate density functional calculations. The structural, electronic, magnetic,
and ferroelectric properties of BiFeO are predicted correctly without
including strong correlation effect in the calculation. Moreover, the
experimentally-observed elongation of cubic perovskite-like lattice along the
[111] direction is correctly reproduced. At high pressure we predicted a
pressure-induced structural transition and the total energy calculations at
expanded lattice show two lower energy ferroelectric phases, closer in energy
to the ground state phase. Band-structure calculations show that BiFeO will
be an insulator in A- and G-type antiferromagnetic phases and a metal in other
magnetic configurations. Chemical bonding in BiFeO has been analyzed using
various tools and electron localization function analysis shows that
stereochemically active lone-pair electrons at the Bi sites are responsible for
displacements of the Bi atoms from the centro-symmetric to the
noncentrosymmetric structure and hence the ferroelectricity. A large
ferroelectric polarization (88.7 C/cm) is predicted in accordance
with recent experimental findings. The net polarization is found to mainly (
98%) originate from Bi atoms. Moreover the large scatter in experimentally
reported polarization values is due to the large anisotropy in the spontaneous
polarization.Comment: 19 pages, 12 figures, 4 table
Breast cancer patients' clinical outcome measures are associated with Src kinase family member expression
<p>BACKGROUND: This study determined mRNA expression levels for Src kinase family (SFK) members in breast tissue specimens and assessed protein expression levels of prominent SFK members in invasive breast cancer to establish associations with clinical outcome. Ki67 was investigated to determine association between SFK members and proliferation.</p>
<p>METHODS: The mRNA expression levels were assessed for eight SFK members by quantitative real-time PCR. Immunohistochemistry was performed for c-Src, Lyn, Lck and Ki67.</p>
<p>RESULTS: mRNA expression was quantified in all tissue samples. SRC and LYN were the most highly expressed in malignant tissue. LCK was more highly expressed in oestrogen receptor (ER)-negative, compared with ER-positive tumours. High cytoplasmic Src kinase protein expression was significantly associated with decreased disease-specific survival. Lyn was not associated with survival at any cellular location. High membrane Lck expression was significantly associated with improved survival. Ki67 expression correlated with tumour grade and nuclear c-Src, but was not associated with survival.</p>
<p>CONCLUSIONS: All eight SFK members were expressed in different breast tissues. Src kinase was highest expressed in breast cancer and had a negative impact on disease-specific survival. Membrane expression of Lck was associated with improved clinical outcome. High expression of Src kinase correlated with high proliferation.</p>
On L<sup>p</sup>-improving measures
© European Mathematical Society. We give criteria for establishing that a measure is Lp-improving. Many Riesz product measures and Cantor measures satisfy this criteria, as well as certain Markov measures
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