3,780 research outputs found
Universal relationship between crystallinity and irreversibility field of MgB2
The relationship between irreversibility field, Hirr, and crystallinity of
MgB2 bulks including carbon substituted samples was studied. The Hirr was found
to increase with an increase of FWHM of MgB2 (110) peak, which corresponds to
distortion of honeycomb boron sheet, and their universal correlation was
discovered even including carbon substituted samples. Excellent Jc
characteristics under high magnetic fields were observed in samples with large
FWHM of (110) due to the enhanced intraband scattering and strengthened grain
boundary flux pinning. The relationship between crystallinity and Hirr can
explain the large variation of Hirr for MgB2 bulks, tapes, single crystals and
thin films.Comment: 3 pages, 4 figures, to be published in Appl. Phys. Lett. (in press
Optical conductivity in the CuO double chains of PrBa_2Cu_4O_8: Consequences of charge fluctuation
We calculate the optical conductivity of the CuO double chains of
PrBaCuO by the mean-field approximation for the coupled two-chain
Hubbard model around quarter filling. We show that the 40 meV peak
structure, spectral shape, and small Drude weight observed in experiment are
reproduced well by the present calculation provided that the stripe-type charge
ordering presents. We argue that the observed anomalous optical response may be
due to the presence of stripe-type fluctuations of charge carriers in the CuO
double chains; the fast time scale of the optical measurement should enable one
to detect slowly fluctuating order parameters as virtually a long-range order.Comment: 7 pages, 5 eps figure
Biaxial magnetic alignment in twinned REBa[2]Cu[3]O[y]superconductors
Biaxial magnetic alignment of REBa[2]Cu[3]O[y] (RE123, RE = Y, Nd, Sm, Dy, and Er) superconductor powders containing twin microstructures was demonstrated. Appropriate choice of RE effectively improved the degrees of in-plane and c-axis orientation in RE123 powder samples aligned under modulated rotating magnetic fields at room temperature. From the relationship between the magnetic field strength and the degrees of orientation, it is concluded that heavy RE ions induced the improvement of the in-plane magnetic anisotropies in RE123 grains with twin microstructures
Dimensionality-driven spin-flop transition in quasi-one-dimensional PrBa2Cu4O8
In the quasi-one-dimensional cuprate PrBaCuO, the Pr cations
order antiferromagnetically at 17 K in zero field. Through a combination of
magnetic susceptibility, torque magnetometry, specific heat and interchain
transport measurements, the anisotropic temperature-magnetic field phase
diagram associated with this ordering has been mapped out. A low-temperature
spin-flop transition in the Pr sub-lattice is found to occur at the same
magnetic field strength and orientation as a dimensional crossover in the
ground state of the metallic CuO chains. This coincidence suggests that the
spin reorientation is driven by a change in the anisotropic
Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction induced by a corresponding
change in effective dimensionality of the conduction electrons.Comment: 8 pages, 8 figure
Anomalous behaviors of the charge and spin degrees of freedom in the CuO double chains of PrBaCuO
The density-matrix renormalization-group method is used to study the
electronic states of a two-chain Hubbard model for CuO double chains of
PrBaCuO. We show that the model at quarter filling has the charge
ordered phases with stripe-type and in-line--type patterns in the parameter
space, and in-between, there appears a wide region of vanishing charge gap; the
latter phase is characteristic of either Tomonaga-Luttinger liquid or a
metallic state with a spin gap. We argue that the low-energy electronic state
of the CuO double chains of PrBaCuO should be in the metallic state
with a possibly small spin gap.Comment: REVTEX 4, 10 pages, 9 figures; submitted to PR
Structural Features of Layered Iron Pnictide Oxides (Fe2As2)(Sr4M2O6)
Structural features of newly found perovskite-based iron pnictide oxide
system have been systematically studied. Compared to REFePnO system,
perovskite-based system tend to have lower Pn-Fe-Pn angle and higher pnictogen
height owing to low electronegativity of alkaline earth metal and small
repulsive force between pnictogen and oxygen atoms. As-Fe-As angles of
(Fe2As2)(Sr4Cr2O6), (Fe2As2)(Sr4V2O6) and (Fe2Pn2)(Sr4MgTiO6) are close to
ideal tetrahedron and those pnictogen heights of about 1.40 A are close to
NdFeAsO with optimized carrier concentration. These structural features of this
system may leads to realization of high Tc superconductivity.Comment: 3pages, 2figures, 1table, proceedings of M2S 200
The great ideas of biology: Exploration through experimentation in an undergraduate lab course
We developed an introductory laboratory course to provide a visceral experience that aims at getting students truly excited about scientific study of the living world. Our vehicle to do that was to focus on what Paul Nurse dubbed “the great ideas of biology” rather than an approach to biology that celebrates specific factual knowledge. To that end, we developed eight diverse experimental
modules, each of which highlights a key biological concept and gives an opportunity to use theory to generate testable hypotheses, to perform high quality measurements to test those hypotheses (some of which are clearly wrong), and to perform sophisticated computational data analysis. Some
modules incorporate modern microscopy and computational techniques in classic experiments, such as bacterial growth and the Luria‐Delbrück experiment, while others address current research questions using methods like optogenetics and single molecule measurements. We have offered the course eight times, and in the most recent edition of the course, we conducted pre/post‐course interviews and
attitude surveys. The students, both bio and non‐bio majors alike, reported being captivated by seeing life occur across the broad range of experiments and model organisms. We observed demonstrable development of their curiosity and enthusiasm for biology. Additionally, we found that
prior to the course, students had only vague notions about what it means to make quantitative biological measurements and interpret them. They completed the course with a clearer understanding of scientific inquiry in biology and the skills and confidence to actually perform and interpret measurements in living systems
Spin dynamics and antiferromagnetic order in PrBa2Cu4O8 studied by Cu nuclear respnance
Results of the nuclear resonance experiments for the planar Cu sites in
PrBa2Cu4O8 are presented. The NMR spectrum at 1.5 K in zero magnetic field
revealed an internal field of 6.1 T, providing evidence for an
antiferromagnetic order of the planar Cu spins. This confirms that the CuO2
planes are insulating, therefore, the metallic conduction in this material is
entirely due to the one-dimensional zigzag Cu2O2 chains. The results of the
spin-lattice relaxation rates measured by zero field NQR above 245 K in the
paramagnetic state are explained by the theory for a Heisenberg model on a
square lattice.Comment: 4 pages, 2 figure
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