4,025 research outputs found
Stability of Spinmotive Force in Perpendicularly Magnetized Nanowires under High Magnetic Fields
Spinmotive force induced by domain wall motion in perpendicularly magnetized
nanowires is numerically demonstrated. We show that using nanowires with large
magnetic anisotropy can lead to a high stability of spinmotive force under
strong magnetic fields. We observe spinmotive force in the order of tens of
microvolt in a multilayered Co/Ni nanowire and in the order of several hundred
microvolt in a FePt nanowire; the latter is two orders of magnitude greater
than that in permalloy nanowires reported previously. The narrow structure and
low mobility of a domain wall under magnetic fields in perpendicularly
magnetized nanowires permits downsizing of spinmotive force devices.Comment: submitted to Applied Physics Letter
The table mountain 8-mm-wavelength interferometer
The system components, performance, and calibration of two element radio interferometer operating at 8.33 mm wavelength are discussed. The interferometer employs a 5.5 m and a 3 m diameter antenna on an east-west baseline of 60 or 120 m, yielding fringe spacings at transit of 28 or 14 in. respectively. The broad intermediate frequency bandpass of 100 to 350 MHz and the system noise temperature of 500 K provide high sensitivity for the measurement of continuum sources. The interferometer has been used for high resolution studies of the planets and the Sun, and it is currently being adapted to study solar flare emissions at high spatial and time resolution
Spin accumulation created electrically in an n-type germanium channel using Schottky tunnel contacts
Using high-quality FeSi/-Ge Schottky-tunnel-barrier contacts, we
study spin accumulation in an -type germanium (-Ge) channel. In the
three- or two-terminal voltage measurements with low bias current conditions at
50 K, Hanle-effect signals are clearly detected only at a forward-biased
contact. These are reliable evidence for electrical detection of the spin
accumulation created in the -Ge channel. The estimated spin lifetime in
-Ge at 50 K is one order of magnitude shorter than those in -Si reported
recently. The magnitude of the spin signals cannot be explained by the commonly
used spin diffusion model. We discuss a possible origin of the difference
between experimental data and theoretical values.Comment: 4 pages, 3 figures, To appear in J. Appl. Phy
Pressure-induced phase transition and bi-polaronic sliding in a hole-doped Cu_2O_3 ladder system
We study a hole-doped two-leg ladder system including metal ions, oxygen, and
electron-lattice interaction, as a model for Sr_{14-x}Ca_xCu_{24}O_{41-\delta}.
Single- and bi-polaronic states at 1/4-hole doping are modeled as functions of
pressure by applying an unrestricted Hartree-Fock approximation to a multiband
Peierls-Hubbard Hamiltonian. We find evidence for a pressure-induced phase
transition between single-polaron and bi-polaron states. The electronic and
phononic excitations in those states, including distinctive local lattice
vibrational modes, are calculated by means of a direct-space Random Phase
approximation. Finally, as a function of pressure, we identify a transition
between site- and bond-centered bi-polarons, accompanied by a soft mode and a
low-energy charge-sliding mode. We suggest comparisons with available
experimented data
Effects of tape covering and vine vigor on development of surface callus in girdle of grapevine
The effects of vine vigor (shoot growth) and covering the girdle surface with plastic tape on the development of a surface callus (SC) in the girdle of grapevine were studied by histological observation. The SC was formed in a tape-covering treatment but was not formed unless the girdle surface was covered with plastic tape (exposing treatment). Histological observation revealed that in the tape-covering treatment, callus cells developed mainly from the ray parenchyma cells on the girdle surface 2 days after girdling (DAG), leading to the formation of the SC, which grew and filled the girdle portion by 7 DAG. When 16 vines were divided into three categories based on scaffold branch length, vines with 7.5 m scaffold branches developed shorter shoots with smaller internode diameters than did vines with 4.5 and 6.0 m scaffold branches. In vines with 7.5 m scaffold branches, the SC covered a smaller area of the girdle surface than in vines with 4.5 and 6.0 m scaffold branches. The length and diameter of the shoot were significantly correlated (r2 = 0.75** and 0.70**, respectively) with the ratio of the girdle area covered by the SC to the whole girdle area (SC covering ratio). These results show that the SC originates mainly from the ray parenchyma cells and that SC development is strongly affected by vine vigor. Consequently, to ensure SC development, girdling should be done by tape covering in vines with shoot diameters larger than 8 mm.
Dimensionality and Irreversibility Field in YBa_2Cu_3O_7 Films (High Field Superconductors)
In order to investigate the relationship between the flux pinning and dimensionality, the critical current density J_c for YBa_2Cu_3O_7 films was measured as a function of temperature, field and tilt angle between field and c-axis. The kink anomaly in the temperature dependence of J_c for B⊥c was observed as the dimensional crossover from 3D extrinsic pinning to 2D intrinsic pinning. The irreversibility field B_i for B//c was measured in fields up to 23T and estimated to be 90T at 30K using the scaling law of the pinning force densities. The enhancement of B_i from a power law (1-T/T_c)^n with n≈1.5 for B//c was observed below 40K. This suggests the formation of the 2-dimensional pancake vortex in YBa_2Cu_3O_7
A checklist of known ant species of Laos (Hymenoptera: Formicidae)
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