11,835 research outputs found
Airborne lidar observations of Arctic polar stratospheric clouds
Polar stratospheric clouds (PSC's) have been detected repeatedly during Arctic and Antarctic winters since 1978/1979 by the SAM II (Stratospheric Aerosol Measurement II) instrument aboard the NIMBUS-7 satellite. PSC's are believed to form when supercooled sulfuric acid droplets freeze, and subsequently grow by deposition of ambient water vapor as the local stratospheric temperature falls below the frost point. In order to study the characteristics of PSC's at higher spatial and temporal resolution than that possible from the satellite observations, aircraft missions were conducted within the Arctic polar night vortex in Jan. 1984 and Jan. 1986 using the NASA Langley Research Center airborne dual polarization ruby lidar system. A synopsis of the 1984 and 1986 PSC observations is presented illustrating short range spatial changes in cloud structure, the variation of backscatter ratio with temperature, and the depolarization characterics of cloud layers. Implications are noted with regard to PSC particle characteristics and the physical process by which the clouds are thougth to form
Few-electron quantum dots in III-V ternary alloys: role of fluctuations
We study experimentally the electron transport properties of gated quantum
dots formed in InGaAs/InP and InAsP/InP quantum well structures grown by
chemical-beam epitaxy. For the case of the InGaAs quantum well, quantum dots
form directly underneath narrow gate electrodes due to potential fluctuations.
We measure the Coulomb-blockade diamonds in the few-electron regime of a single
quantum dot and observe photon-assisted tunneling peaks under microwave
irradiation. A singlet-triplet transition at high magnetic field and
Coulomb-blockade effects in the quantum Hall regime are also observed. For the
InAsP quantum well, an incidental triple quantum dot forms also due to
potential fluctuations within a single dot layout. Tunable quadruple points are
observed via transport measurements.Comment: 3.3 pages, 3 figures. Added two new subfigures, new references, and
improved the tex
Panel discussion
"The Importance of Being Predictable" by John B. Taylor -- "Monetary Policy Under Uncertainty" by Ben S. Bernanke -- "The Importance of Being Predictable" by William PooleMonetary policy
Panel discussion monetary policy modeling: where are we and where should we be going?
Monetary policy ; Inflation (Finance) ; Econometric models
Reducing Polarization Mode Dispersion With Controlled Polarization Rotations
One of the fundamental limitations to high bit rate, long distance,
telecommunication in optical fibers is Polarization Mode Dispersion (PMD). Here
we introduce a conceptually new method to reduce PMD in optical fibers by
carrying out controlled rotations of polarization at predetermined locations
along the fiber. The distance between these controlled polarization rotations
must be less than both the beat length and the mode coupling length of the
fiber. This method can also be combined with the method in which the fiber is
spun while it drawn. The incidence of imperfections on the efficiency of the
method is analysed.Comment: 4 page
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