707 research outputs found
Structural characterization of YBa(2)Cu(3)O(7)/Y(2)O(3) composite films
Using 4-circle x-ray diffraction and transmission electron microscopy we have
studied the microstructure and in-plane orientation of the phases present in
thin film composite mixtures of YBa(2)Cu(3)O(7) and Y(2)O(3). We see a high
degree of in-plane orientation and have verified a previous prediction for the
in-plane order of Y(2)BaCuO(5) on (110) MgO. Transmission electron microscopy
shows the composite films to be a mixture of two phases, with YBCO grain sizes
of 1 micron. We have also compared our observations of the in-plane order to
the predictions of a modified near coincidence site lattice model.Comment: To be published in Journal of Materials Research, (4 pages, 4 jpeg
figures
Proximity effect in Nb-Mo layered films: Transition temperature and critical current dependence on period
The behavior of the transition temperature and critical current density for a
Mo/Nb repeated bilayer system as a function of the number of periods was
explored. The measured values of the transition temperature are compared to the
theoretical predictions for the proximity effect in the dirty limit. We find
that the transition temperature does not decrease as the number of periods
increase. In addition, inductive critical current density measurements also
show a scaling that indicates the superconductivity properties are not
dependent on the number of bilayers.Comment: 13 pages, 6 figures, to be published Journal of Applied Physic
Techniques to stimulate and interrogate cell–cell adhesion mechanics
Cell–cell adhesions maintain the mechanical integrity of multicellular tissues and have recently been found to act as mechanotransducers, translating mechanical cues into biochemical signals. Mechanotransduction studies have primarily focused on focal adhesions, sites of cell-substrate attachment. These studies leverage technical advances in devices and systems interfacing with living cells through cell–extracellular matrix adhesions. As reports of aberrant signal transduction originating from mutations in cell–cell adhesion molecules are being increasingly associated with disease states, growing attention is being paid to this intercellular signaling hub. Along with this renewed focus, new requirements arise for the interrogation and stimulation of cell–cell adhesive junctions. This review covers established experimental techniques for stimulation and interrogation of cell–cell adhesion from cell pairs to monolayers
A high-field adiabatic fast passage ultracold neutron spin flipper for the UCNA experiment
The UCNA collaboration is making a precision measurement of the β asymmetry (A) in free neutron decay using polarized ultracold neutrons (UCN). A critical component of this experiment is an adiabatic fast passage neutron spin flipper capable of efficient operation in ambient magnetic fields on the order of 1 T. The requirement that it operate in a high field necessitated the construction of a free neutron spin flipper based, for the first time, on a birdcage resonator. The design, construction, and initial testing of this spin flipper prior to its use in the first measurement of A with UCN during the 2007 run cycle of the Los Alamos Neutron Science Center's 800 MeV proton accelerator is detailed. These studies determined the flipping efficiency of the device, averaged over the UCN spectrum present at the location of the spin flipper, to be ϵ(overbar) = 0.9985(4)
Measurement of the half-life of the T= mirror decay of Ne and its implication on physics beyond the standard model
The superallowed mixed mirror decay
of Ne to F is excellently suited for high precision studies of
the weak interaction. However, there is some disagreement on the value of the
half-life. In a new measurement we have determined this quantity to be
= s, which differs
from the previous world average by 3 standard deviations. The impact of this
measurement on limits for physics beyond the standard model such as the
presence of tensor currents is discussed.Comment: 5 pages, 3 figures, 1 tabl
emiT: an apparatus to test time reversal invariance in polarized neutron decay
We describe an apparatus used to measure the triple-correlation term (\D
\hat{\sigma}_n\cdot p_e\times p_\nu) in the beta-decay of polarized neutrons.
The \D-coefficient is sensitive to possible violations of time reversal
invariance. The detector has an octagonal symmetry that optimizes
electron-proton coincidence rates and reduces systematic effects. A beam of
longitudinally polarized cold neutrons passes through the detector chamber,
where a small fraction beta-decay. The final-state protons are accelerated and
focused onto arrays of cooled semiconductor diodes, while the coincident
electrons are detected using panels of plastic scintillator. Details regarding
the design and performance of the proton detectors, beta detectors and the
electronics used in the data collection system are presented. The neutron beam
characteristics, the spin-transport magnetic fields, and polarization
measurements are also described.Comment: 15 pages, 13 figure
Unconventional one-magnon scattering resistivity in half metals
Low-temperature resistivity of half-metals is investigated. To date it has
been discussed that the one-magnon scattering process in half-metals is
irrelevant for low-temperature resistivity, due to the fully spin-polarized
electronic structure at the ground state. If one takes into account the
non-rigid-band behavior of the minority band due to spin fluctuations at finite
temperatures, however, the unconventional one-magnon scattering process is
shown to be most relevant and gives T^3 dependence in resistivity. This
behavior may be used as a crucial test in the search for half-metallic
materials which are potentially important for applications. Comparison with
resistivity data of
La_1-x Sr_x MnO_3 as candidates for half-metals shows good agreement.Comment: 4 pages, including 5 eps figures. To be published in J. Phys. Soc.
Jpn. vol. 69 No. 7 (2000
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