17,852 research outputs found
Comparison of different methods for estimating snowcover in forested, mountainous basins using LANDSAT (ERTS) images
Snow-covered areas on LANDSAT (ERTS) images of the Santiam River basin, Oregon, and other basins in Washington were measured using several operators and methods. Seven methods were used: (1) Snowline tracing followed by measurement with planimeter, (2) mean snowline altitudes determined from many locations, (3) estimates in 2.5 x 2.5 km boxes of snow-covered area with reference to snow-free images, (4) single radiance-threshold level for entire basin, (5) radiance-threshold setting locally edited by reference to altitude contours and other images, (6) two-band color-sensitive extraction locally edited as in (5), and (7) digital (spectral) pattern recognition techniques. The seven methods are compared in regard to speed of measurement, precision, the ability to recognize snow in deep shadow or in trees, relative cost, and whether useful supplemental data are produced
CW and pulsed electrically detected magnetic resonance spectroscopy at 263 GHz/12 T on operating amorphous silicon solar cells
Here we describe a new high frequency/high field continuous wave and pulsed
electrically detected magnetic resonance (CW EDMR and pEDMR) setup, operating
at 263 GHz and resonance fields between 0 and 12 T. Spin dependent transport in
illuminated hydrogenated amorphous silicon p-i-n solar cells at 5 K and 90 K
was studied by in operando 263 GHz CW and pEDMR alongside with complementary
X-band CW EDMR. Benefiting from the superior resolution at 263 GHz, we were
able to better resolve EDMR signals originating from spin dependent hopping and
recombination processes. 5 K EDMR spectra were found to be dominated by
conduction and valence band tale states involved in spin dependent hopping,
with additional contributions from triplet exciton states. 90 K EDMR spectra
could be assigned to spin pair recombination involving conduction band tail
states and dangling bonds as dominating spin dependent transport process, with
additional contributions from valence band tail and triplet exciton states.Comment: 8 pages, 4 figure
Snow wetness measurements for melt forecasting
A microwave technique for directly measuring snow pack wetness in remote installations is described. The technique, which uses satellite telemetry for data gathering, is based on the attenuation of a microwave beam in transmission through snow
Design and Performance of the CMS Pixel Detector Readout Chip
The readout chip for the CMS pixel detector has to deal with an enormous data
rate. On-chip zero suppression is inevitable and hit data must be buffered
locally during the latency of the first level trigger. Dead-time must be kept
at a minimum. It is dominated by contributions coming from the readout. To keep
it low an analog readout scheme has been adopted where pixel addresses are
analog coded. We present the architecture of the final CMS pixel detector
readout chip with special emphasis on the analog readout chain. Measurements of
its performance are discussed.Comment: 8 pages, 11 figures. Contribution to the Proceedings of the Pixel2005
Workshop, Bonn, German
Hubble Space Telescope Ultraviolet Imaging and High-Resolution Spectroscopy of Water Photodissociation Products in Comet Hyakutake (C/1996 B2)
Comet Hyakutake (C/1996 B2) provided a target of opportunity for performing a systematic study of water photodissociation products in which we obtained data from three instruments on the Hubble Space Telescope (HST). The HST Goddard High Resolution Spectrograph (GHRS) was used to measure the line profile of hydrogen Lyα (H Lyα) at six locations around the coma of the comet, ranging from the nucleus to a displacement of 100,000 km, and covering different directions compared with the comet-sun line. GHRS yielded line profiles with a spectral resolution (FWHM ~4 km s^(-1)) that was a factor of 2-3 better than any previous H Lyα or Hα ground-based measurements. The Wide Field Planetary Camera 2 (WFPC2) and the Woods filter were used to obtain H Lyα images of the inner coma. The faint object spectrograph (FOS) was used to determine the OH production rate and monitor its variation throughout the HST observing sequence. The GHRS H Lyα line profiles show the behavior of a line profile that is optically thick in the core for positions near the nucleus (<5000 km) and gradually becoming more optically thin at larger displacements and lower column abundances. A composite H Lyα image constructed from four separate WFPC2 exposures is consistent with the relative fluxes seen in GHRS observations and clearly shows the dayside enhancement of a solar illuminated optically thick coma. These data were analyzed self-consistently to test our understanding of the detailed physics and chemistry of the expanding coma and our ability to obtain accurate water production rates from remote observations of gaseous hydrogen (H) and hydroxyl (OH), the major water dissociation products. Our hybrid kinetic/hydrodynamic model of the coma combined with a spherical radiative transfer calculation is able to account for (1) the velocity distribution of H atoms, (2) the spatial distribution of the H Lyα emission in the inner coma, and (3) the absolute intensities of H and OH emissions, giving a water production rate of (2.6 ± 0.4) × 10^(29) s^(-1) on 1996 April 4
Kinetics of spin coherence of electrons in -type InAs quantum wells under intense terahertz laser fields
Spin kinetics in -type InAs quantum wells under intense terahertz laser
fields is investigated by developing fully microscopic kinetic spin Bloch
equations via the Floquet-Markov theory and the nonequilibrium Green's function
approach, with all the relevant scattering, such as the electron-impurity,
electron-phonon, and electron-electron Coulomb scattering explicitly included.
We find that a {\em finite} steady-state terahertz spin polarization induced by
the terahertz laser field, first predicted by Cheng and Wu [Appl. Phys. Lett.
{\bf 86}, 032107 (2005)] in the absence of dissipation, exists even in the
presence of all the scattering. We further discuss the effects of the terahertz
laser fields on the spin relaxation and the steady-state spin polarization. It
is found that the terahertz laser fields can {\em strongly} affect the spin
relaxation via hot-electron effect and the terahertz-field-induced effective
magnetic field in the presence of spin-orbit coupling. The two effects compete
with each other, giving rise to {\em non-monotonic} dependence of the spin
relaxation time as well as the amplitude of the steady state spin polarization
on the terahertz field strength and frequency. The terahertz field dependences
of these quantities are investigated for various impurity densities, lattice
temperatures, and strengths of the spin-orbit coupling. Finally, the importance
of the electron-electron Coulomb scattering on spin kinetics is also addressed.Comment: 17 pages, 16 figures, Phys. Rev. B 78, 2008, in pres
Structure of a Complete ATP Synthase Dimer Reveals the Molecular Basis of Inner Mitochondrial Membrane Morphology
We determined the structure of a complete, dimeric F1Fo-ATP synthase from yeast Yarrowia lipolytica mitochondria by a combination of cryo-EM and X-ray crystallography. The final structure resolves 58 of the 60 dimer subunits. Horizontal helices of subunit a in Fo wrap around the c-ring rotor, and a total of six vertical helices assigned to subunits a, b, f, i, and 8 span the membrane. Subunit 8 (A6L in human) is an evolutionary derivative of the bacterial b subunit. On the lumenal membrane surface, subunit f establishes direct contact between the two monomers. Comparison with a cryo-EM map of the F1Fo monomer identifies subunits e and g at the lateral dimer interface. They do not form dimer contacts but enable dimer formation by inducing a strong membrane curvature of ∼100°. Our structure explains the structural basis of cristae formation in mitochondria, a landmark signature of eukaryotic cell morphology
Power dependence of pure spin current injection by quantum interference
We investigate the power dependence of pure spin current injection in GaAs
bulk and quantum-well samples by a quantum interference and control technique.
Spin separation is measured as a function of the relative strength of the two
transition pathways driven by two laser pulses. By keeping the relaxation time
of the current unchanged, we are able to relate the spin separation to the
injected average velocity. We find that the average velocity is determined by
the relative strength of the two transitions in the same way as in classical
interference. Based on this, we conclude that the density of injected pure spin
current increases monotonically with the excitation laser intensities. The
experimental results are consistent with theoretical calculations based on
Fermi's golden rule.Comment: 6 pages, 4 figure
Single-Electron Effects in a Coupled Dot-Ring System
Aharonov-Bohm oscillations are studied in the magnetoconductance of a
micron-sized open quantum ring coupled capacitively to a Coulomb-blockaded
quantum dot. As the plunger gate of the dot is modulated and tuned through a
conductance resonance, the amplitude of the Aharonov-Bohm oscillations in the
transconductance of the ring displays a minimum. We demonstrate that the effect
is due to a single-electron screening effect, rather than to dephasing.
Aharonov-Bohm oscillations in a quantum ring can thus be used for the detection
of single charges.Comment: 5 pages, 3 figure
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