1,921 research outputs found
Hall effect of quasi-hole gas in organic single-crystal transistors
Hall effect is detected in organic field-effect transistors, using
appropriately shaped rubrene (C42H28) single crystals. It turned out that
inverse Hall coefficient, having a positive sign, is close to the amount of
electric-field induced charge upon the hole accumulation. The presence of the
normal Hall effect means that the electromagnetic character of the surface
charge is not of hopping carriers but resembles that of a two-dimensional
hole-gas system
Acoustic characteristics of a large scale wind-tunnel model of a jet flap aircraft
The expanding-duct jet flap (EJF) concept is studied to determine STOL performance in turbofan-powered aircraft. The EJF is used to solve the problem of ducting the required volume of air into the wing by providing an expanding cavity between the upper and lower surfaces of the flap. The results are presented of an investigation of the acoustic characteristics of the EJF concept on a large-scale aircraft model powered by JT15D engines. The noise of the EJF is generated by acoustic dipoles as shown by the sixth power dependence of the noise on jet velocity. These sources result from the interaction of the flow turbulence with flap of internal and external surfaces and the trailing edges. Increasing the trailing edge jet from 70 percent span to 100 percent span increased the noise 2 db for the equivalent nozzle area. Blowing at the knee of the flap rather than the trailing edge reduced the noise 5 to 10 db by displacing the jet from the trailing edge and providing shielding from high-frequency noise. Deflecting the flap and varying the angle of attack modified the directivity of the underwing noise but did not affect the peak noise. A forward speed of 33.5 m/sec (110 ft/sec) reduced the dipole noise less than 1 db
Large-scale V/STOL testing
Several facets of large-scale testing of V/STOL aircraft configurations are discussed with particular emphasis on test experience in the Ames 40- by 80-Foot Wind Tunnel. Examples of powered-lift test programs are presented in order to illustrate tradeoffs confronting the planner of V/STOL test programs. Large-scale V/STOL wind-tunnel testing can sometimes compete with small-scale testing in the effort required (overall test time) and program costs because of the possibility of conducting a number of different tests with a single large-scale model where several small-scale models would be required. The benefits of both high- or full-scale Reynolds numbers, more detailed configuration simulation, and number and type of onboard measurements are studied
Critical Scale-invariance in Healthy Human Heart Rate
We demonstrate the robust scale-invariance in the probability density
function (PDF) of detrended healthy human heart rate increments, which is
preserved not only in a quiescent condition, but also in a dynamic state where
the mean level of heart rate is dramatically changing. This scale-independent
and fractal structure is markedly different from the scale-dependent PDF
evolution observed in a turbulent-like, cascade heart rate model. These results
strongly support the view that healthy human heart rate is controlled to
converge continually to a critical state.Comment: 9 pages, 3 figures. Phys. Rev. Lett., to appear (2004
Current distribution inside Py/Cu lateral spin-valve device
We have investigated experimentally the non-local voltage signal (NLVS) in
the lateral permalloy (Py)/Cu/Py spin valve devices with different width of Cu
stripes. We found that NLVS strongly depends on the distribution of the
spin-polarized current inside Cu strip in the vicinity of the Py-detector. To
explain these data we have developed a diffusion model describing spatial (3D)
distribution of the spin-polarized current in the device. The results of our
calculations show that NLVS is decreased by factor of 10 due to spin
flip-scattering occurring at Py/Cu interface. The interface resistivity on
Py/Cu interface is also present, but its contribution to reduction of NLVS is
minor. We also found that most of the spin-polarized current is injected within
the region 30 nm from Py-injector/Cu interface. In the area at Py-detector/Cu
interface, the spin-polarized current is found to flow mainly close on the
injector side, with 1/e exponential decay in the magnitude within the distance
80 nm.Comment: 10 pages, 14 figure
Four-electron shell structures and an interacting two-electron system in carbon nanotube quantum dots
Low-temperature transport measurements have been carried out on single-wall
carbon nanotube quantum dots in a weakly coupled regime in magnetic fields up
to 8 Tesla. Four-electron shell filling was observed, and the magnetic field
evolution of each Coulomb peak was investigated, in which magnetic field
induced spin flip and resulting spin polarization were observed. Excitation
spectroscopy measurements have revealed Zeeman splitting of single particle
states for one electron in the shell, and demonstrated singlet and triplet
states with direct observation of the exchange splitting at zero-magnetic field
for two electrons in the shell, the simplest example of the Hund's rule. The
latter indicates the direct analogy to an artificial He atom.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
Multistable attractors in a network of phase oscillators with three-body interaction
Three-body interactions have been found in physics, biology, and sociology.
To investigate their effect on dynamical systems, as a first step, we study
numerically and theoretically a system of phase oscillators with three-body
interaction. As a result, an infinite number of multistable synchronized states
appear above a critical coupling strength, while a stable incoherent state
always exists for any coupling strength. Owing to the infinite multistability,
the degree of synchrony in asymptotic state can vary continuously within some
range depending on the initial phase pattern.Comment: 5 pages, 3 figure
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