3,512 research outputs found
Magnetic domain fluctuations in an antiferromagnetic film observed with coherent resonant soft x-ray scattering
We report the direct observation of slow fluctuations of helical
antiferromagnetic domains in an ultra-thin holmium film using coherent resonant
magnetic x-ray scattering. We observe a gradual increase of the fluctuations in
the speckle pattern with increasing temperature, while at the same time a
static contribution to the speckle pattern remains. This finding indicates that
domain-wall fluctuations occur over a large range of time scales. We ascribe
this non-ergodic behavior to the strong dependence of the fluctuation rate on
the local thickness of the film.Comment: to appear in Phys. Rev. Let
Soft-Rot Capabilities of the Major Microfungi, Isolated from Douglas-Fir Poles in the Northeast
Four hundred seventeen fungi were isolated from 144 of the 163 Douglas-fir poles (ages 7 to 17 years and treatments CCA, penta and oil, or Cellon®) sampled from transmission lines or storage piles in New York and Pennsylvania. Microfungi predominated and comprised nearly 85% of all isolates. They were isolated primarily from treated zones and were most abundant in older CCA-treated poles in transmission lines. Antrodia carbonica and Postia placenta were the principal basidiomycete decayers and isolated primarily from untreated zones in CCA-treated poles. A limited number of white-rot fungi were isolated from the treated and untreated zones of several poles.Seven of the 12 principal microfungi were established to have soft-rot capabilities. Soft rot was detected anatomically in 23 of the 144 poles in transmission lines. In most cases it was superficial and limited to several outer annual rings; however, it was severe in older CCA-treated poles and involved all of the treated zone and extended several centimeters radially into the untreated zone. Also, soft rot was detected anatomically and soft-rot fungi culturally, in 8 of 12 13-year-old CCA-treated poles that had been fumigated with Vapam 5 or 6 years previously. None was detected in the fumigated penta-treated poles.These data suggest that soft-rot fungi play an important role in decay development in the treated groundline zone of utility poles and should be considered in decay detection programs (culturally) and decisions on the timing of remedial treatments
Reorientation of Spin Density Waves in Cr(001) Films induced by Fe(001) Cap Layers
Proximity effects of 20 \AA thin Fe layers on the spin density waves (SDWs)
in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk
Cr we observe a SDW with its wave vector Q pointing along only one {100}
direction which depends dramatically on the film thickness t_{Cr}. For t_{Cr} <
250 \AA the SDW propagates out-of-plane with the spins in the film plane. For
t_{Cr} > 1000 \AA the SDW propagates in the film plane with the spins
out-of-plane perpendicular to the in-plane Fe moments. This reorientation
transition is explained by frustration effects in the antiferromagnetic
interaction between Fe and Cr across the Fe/Cr interface due to steps at the
interface.Comment: 4 pages (RevTeX), 3 figures (EPS
Ferromagnetic Domain Distribution in Thin Films During Magnetization Reversal
We have shown that polarized neutron reflectometry can determine in a
model-free way not only the mean magnetization of a ferromagnetic thin film at
any point of a hysteresis cycle, but also the mean square dispersion of the
magnetization vectors of its lateral domains. This technique is applied to
elucidate the mechanism of the magnetization reversal of an exchange-biased
Co/CoO bilayer. The reversal process above the blocking temperature is governed
by uniaxial domain switching, while below the blocking temperature the reversal
of magnetization for the trained sample takes place with substantial domain
rotation
Microdeletion of target sites for insulator protein CTCF in a chromosome 11p15 imprinting center in Beckwith-Wiedemann syndrome and Wilms' tumor
We have analyzed several cases of Beckwith-Wiedemann syndrome (BWS) with Wilms' tumor in a familial setting, which give insight into the complex controls of imprinting and gene expression in the chromosome 11p15 region. We describe a 2.2-kbp microdeletion in the H19/insulin-like growth factor 2 (IGF2)-imprinting center eliminating three target sites of the chromatin insulator protein CTCF that we believe here is necessary, but not sufficient, to cause BWS and Wilms' tumor. Maternal inheritance of the deletion is associated with IGF2 loss of imprinting and up-regulation of IGF2 mRNA. However, in at least one affected family member a second genetic lesion (a duplication of maternal 11p15) was identified and accompanied by a further increase in IGF2 rnRNA levels 35-fold higher than control values. Our results suggest that the combined effects of the H19//GF2-imprinting center microdeletion and 11p15 chromosome duplication were necessary for manifestation of BWS
Degeneracy analysis for a super cell of a photonic crystal and its application to the creation of band gaps
A method is introduced to analyze the degeneracy properties of the band
structure of a photonic crystal making use of the super cells. The band
structure associated with a super cell of a photonic crystal has degeneracies
at the edge of the Brillouin zone if the photonic crystal has some kind of
point group symmetry. Both E-polarization and H-polarization cases have the
same degeneracies for a 2-dimensional (2D) photonic crystal. Two theorems are
given and proved. These degeneracies can be lifted to create photonic band gaps
by changing the transform matrix between the super cell and the smallest unit
cell. The existence of the photonic band gaps for many known 2D photonic
crystals is explained through the degeneracy analysis.Comment: 19 pages, revtex4, 14 figures, p
Josephson tunnel junctions with ferromagnetic \Fe_{0.75}\Co_{0.25} barriers
Josephson tunnel junctions with the strong ferromagnetic alloy
\Fe_{0.75}\Co_{0.25} as the barrier material were studied. The junctions were
prepared with high quality down to a thickness range of a few monolayers of
Fe-Co. An oscillation length of between 0
and -Josephson phase coupling and a very short decay length
for the amplitude of the superconducting
pair wave function in the Fe-Co layer were determined. The rapid damping of the
pair wave function inside the Fe-Co layer is caused by the strong ferromagnetic
exchange field and additional magnetic pair breaking scattering. Josephson
junctions with Fe-Co barriers show a significantly increased tendency towards
magnetic remanence and flux trapping for larger thicknesses .Comment: contains 5 figure
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