1,663 research outputs found
Electron Photodetachment from Aqueous Anions. I. Quantum Yields for Generation of Hydrated Electron by 193 and 248 nm Laser Photoexcitation of Miscellaneous Inorganic Anions
Time resolved transient absorption spectroscopy has been used to determine
quantum yields for electron photodetachment in 193 nm and (where possible) 248
nm laser excitation of miscellaneous aqueous anions, including
hexacyanoferrate(II), sulfate, sulfite, halide anions (Cl-, Br-, and I-),
pseudohalide anions (OH-, HS-, CNS-), and several common inorganic anions for
which no quantum yields have been reported heretofore: SO3=, NO2-, NO3-, ClO3-
and ClO4-. Molar extinction coefficients for these anions and photoproducts of
electron detachment from these anions at the excitation wavelengths were also
determined. These results are discussed in the context of recent ultrafast
kinetic studies and compared with the previous data obtained by product
analyses. We suggest using electron photodetachment from the aqueous halide and
pseudohalide anions as actinometric standard for time-resolved studies of
aqueous photosystems in the UV.Comment: 41 page, 6 figures; supplement: 3 pages, 12 figures; to be submitted
to J. Phys. Chem.
Helicopter low-speed yaw control
A system for improving yaw control at low speeds consists of one strake placed on the upper portion of the fuselage facing the retreating rotor blade and another strake placed on the lower portion of the fuselage facing the advancing rotor blade. These strakes spoil the airflow on the helicopter tail boom during hover, low speed flight, and right or left sidewards flight so that less side thrust is required from the tail rotor
Two-dimensional aerodynamic characteristics of several polygon-shaped cross-sectional models applicable to helicopter fuselages
A wind-tunnel investigation was conducted to determine 2-D aerodynamic characteristics of nine polygon-shaped models applicable to helicopter fuselages. The models varied from 1/2 to 1/5 scale and were nominally triangular, diamond, and rectangular in shape. Side force and normal force were obtained at increments of angle of flow incidence from -45 to 90 degrees. The data were compared with results from a baseline UH-60 tail-boom cross-section model. The results indicate that the overall shapes of the plots of normal force and side force were similar to the characteristic shape of the baseline data; however, there were important differences in magnitude. At a flow incidence of 0 degrees, larger values of normal force for the polygon models indicate an increase in fuselage down load of 1 to 2.5 percent of main-rotor thrust compared with the baseline value. Also, potential was indicated among some of the configurations to produce high fuselage side forces and yawing moments compared with the baseline model
Surface Roughness Dominated Pinning Mechanism of Magnetic Vortices in Soft Ferromagnetic Films
Although pinning of domain walls in ferromagnets is ubiquitous, the absence
of an appropriate characterization tool has limited the ability to correlate
the physical and magnetic microstructures of ferromagnetic films with specific
pinning mechanisms. Here, we show that the pinning of a magnetic vortex, the
simplest possible domain structure in soft ferromagnets, is strongly correlated
with surface roughness, and we make a quantitative comparison of the pinning
energy and spatial range in films of various thickness. The results demonstrate
that thickness fluctuations on the lateral length scale of the vortex core
diameter, i.e. an effective roughness at a specific length scale, provides the
dominant pinning mechanism. We argue that this mechanism will be important in
virtually any soft ferromagnetic film.Comment: 4 figure
Electrical Detection of Spin Accumulation at a Ferromagnet-Semiconductor Interface
We show that the accumulation of spin-polarized electrons at a forward-biased
Schottky tunnel barrier between Fe and n-GaAs can be detected electrically. The
spin accumulation leads to an additional voltage drop across the barrier that
is suppressed by a small transverse magnetic field, which depolarizes the spins
in the semiconductor. The dependence of the electrical accumulation signal on
magnetic field, bias current, and temperature is in good agreement with the
predictions of a drift-diffusion model for spin-polarized transport.Comment: Submitted to Phys. Rev. Let
Transient x-ray absorption spectroscopy of hydrated halogen atom
Time-resolved x-ray absorption spectroscopy monitors the transient species
generated by one-photon detachment of an electron from aqueous bromide.
Hydrated bromine atoms with a lifetime of ca. 17 ns were observed, nearly half
of which react with excess Br- to form Br2-. The K-edge spectra of the Br atom
and Br2- anion exhibit distinctive resonant transitions that are absent for the
Br- precursor. The absorption spectra indicate that the solvent shell around a
Br0 atom is defined primarily by hydrophobic interactions, in agreement with a
Monte Carlo simulation of the solvent structure.Comment: 6 pages, 4 figures + supplement, will be submitted to PR
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