6,599 research outputs found
Localized Distributions of Quasi Two-Dimensional Electronic States near Defects Artificially Created at Graphite Surfaces in Magnetic Fields
We measured the local density of states of a quasi two-dimensional electron
system (2DES) near defects, artificially created by Ar-ion sputtering, on
surfaces of highly oriented pyrolytic graphite (HOPG) with scanning tunneling
spectroscopy (STS) in high magnetic fields. At valley energies of the Landau
level spectrum, we found two typical localized distributions of the 2DES
depending on the defects. These are new types of distributions which are not
observed in the previous STS work at the HOPG surface near a point defect [Y.
Niimi \textit{et al}., Phys. Rev. Lett. {\bf 97}, 236804 (2006).]. With
increasing energy, we observed gradual transformation from the localized
distributions to the extended ones as expected for the integer quantum Hall
state. We show that the defect potential depth is responsible for the two
localized distributions from comparison with theoretical calculations.Comment: 4 pages, 3 figure
Cloud optical thickness and effective particle radius derived from transmitted solar radiation measurements : Comparison with cloud radar observations
A method is presented for determining the optical thickness and effective particle radius of stratiform clouds containing liquid water drops in the absence of drizzle from transmitted solar radiation measurements. The procedure compares measurements of the cloud transmittance from the ground at water-absorbing and nonabsorbing wavelengths with lookup tables of the transmittance precomputed for plane-parallel, vertically homogeneous clouds. The optical thickness derived from the cloud transmittance may be used to retrieve vertical profiles of cloud microphysics in combination with the radar reflectivity factor. To do this, we also present an algorithm for solving the radar equation with a constraint of the optical thickness at the visible wavelength. Observations of clouds were made in August and September 2003 at Koganei, Tokyo, Japan, using a PREDE i-skyradiometer and a 95-GHz cloud radar Super Polarimetric Ice Crystal Detection and Explication Radar (SPIDER). The optical thickness and effective radius of water clouds were derived from the i-skyradiometer. Then, the vertical profile of the effective radius was retrieved from SPIDER, using the optical thickness determined from the i-skyradiometer. We found that the effective radii derived by using these two instruments were in good agreement
Thermal switching rate of a ferromagnetic material with uniaxial anisotropy
The field dependence of the thermal switching rate of a ferromagnetic
material with uniaxial anisotropy was studied by solving the Fokker-Planck
equation. We derived the analytical expression of the thermal switching rate
using the mean first-passage time approach, and found that Brown's formula
[Phys. Rev. 130, 1677 (1963)] is applicable even in the low barrier limit by
replacing the attempt frequency with the proper factor which is expressed by
the error function.Comment: 5 pages, 2 figure
Synchronization of weakly perturbed Markov chain oscillators
Rate processes are simple and analytically tractable models for many
dynamical systems which switch stochastically between a discrete set of quasi
stationary states but they may also approximate continuous processes by coarse
grained, symbolic dynamics. In contrast to limit cycle oscillators which are
weakly perturbed by noise, the stochasticity in such systems may be strong and
more complicated system topologies than the circle can be considered. Here we
employ second order, time dependent perturbation theory to derive expressions
for the mean frequency and phase diffusion constant of discrete state
oscillators coupled or driven through weakly time dependent transition rates.
We also describe a method of global control to optimize the response of the
mean frequency in complex transition networks.Comment: 16 pages, 7 figure
Revision of empirical electric field modeling in the inner magnetosphere using Cluster data
Using Cluster data from the Electron Drift (EDI) and the Electric Field and Wave (EFW) instruments, we revise our empirically-based, inner-magnetospheric electric field (UNH-IMEF) model at 22.662 mV/m; K-p\u3c1, 1K(p)\u3c2, 2K(p)\u3c3, 3K(p)\u3c4, 4K(p)\u3c5, and K(p)4(+). Patterns consist of one set of data and processing for smaller activities, and another for higher activities. As activity increases, the skewed potential contour related to the partial ring current appears on the nightside. With the revised analysis, we find that the skewed potential contours get clearer and potential contours get denser on the nightside and morningside. Since the fluctuating components are not negligible, standard deviations from the modeled values are included in the model. In this study, we perform validation of the derived model more extensively. We find experimentally that the skewed contours are located close to the last closed equipotential, consistent with previous theories. This gives physical context to our model and serves as one validation effort. As another validation effort, the derived results are compared with other models/measurements. From these comparisons, we conclude that our model has some clear advantages over the others
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