1,118 research outputs found
The effects of trap fishing in coral reef habitats: a preliminary analysis [abstract]; Los effectos de la pesca con trampas en los arrecifes de coral y en los habitat associados con estos: analysis preliminares [resumen]
Multi-Electron-Transfer Catalysts Needed for Artificial Photosynthesis
Journal: 2011 MRS Fall Meeting
Manuscript ID: Draft
Manuscript Type: Symposium E
Date Submitted by the Author: n/a
Complete List of Authors: Vickers, James; Emory University, Chemistry
Lv, Hongjin; Emory University, Chemistry
Zhuk, Petro; National Aviation University,
Geletii, Yurii; Emory University, Chemistry
Hill, Craig; Emory University, Chemistry
Keywords: catalytic, kinetics, oxidationWe report a study on catalytic water oxidation by cobalt in oxygen ligand environments
because such systems are as promising as any in the water oxidation component of solar fuel
production. We have re-examined the catalytic activity of Co(II) in aqueous solution using either
[Ru(bpy)3]3+ as a stoichiometric oxidant or in visible-light-driven reactions with persulfate as a
sacrificial electron acceptor. In both systems a distinctive induction period is observed. A simple
kinetic model is proposed that describes the experimental data well. The presence of an
induction period is explained by relatively slow formation of the true catalyst from
aquacobalt(II)
Observation of the screening signature in the lateral photovoltage of electrons in the Quantum Hall regime
The lateral photovoltage generated in the plane of a two-dimensional electron
system (2DES) by a focused light spot, exhibits a fine-structure in the quantum
oscillations in a magnetic field near the Quantum Hall conductivity minima. A
double peak structure occurs near the minima of the longitudinal conductivity
oscillations. This is the characteristic signature of the interplay between
screening and Landau quantization.Comment: 4 pages, 4 figures, to be published in Phys. Rev.
Behavior of the giant-dipole resonance in Sn and Pb at high excitation energ
The properties of the giant-dipole resonance (GDR) are calculated as a
function of excitation energy, angular momentum, and the compound nucleus
particle decay width in the nuclei Sn and Pb, and are compared
with recent experimental data. Differences observed in the behavior of the
full-width-at-half-maximum of the GDR for Sn and Pb are
attributed to the fact that shell corrections in Pb are stronger than
in Sn, and favor the spherical shape at low temperatures. The effects
shell corrections have on both the free energy and the moments of inertia are
discussed in detail. At high temperature, the FWHM in Sn exhibits
effects due to the evaporation width of the compound nucleus, while these
effects are predicted for Pb.Comment: 28 pages in RevTeX plus eight postscript figures. Submitted to Nucl.
Phys.
Drum vortons in high density QCD
Recently it was shown that high density QCD supports of number of topological
defects. In particular, there are U(1)_Y strings that arise due to K^0
condensation that occurs when the strange quark mass is relatively large. The
unique feature of these strings is that they possess a nonzero K^+ condensate
that is trapped on the core. In the following we will show that these strings
(with nontrivial core structure) can form closed loops with conserved charge
and currents trapped on the string worldsheet. The presence of conserved
charges allows these topological defects, called vortons, to carry angular
momentum, which makes them classically stable objects. We also give arguments
demonstrating that vortons carry angular momentum very efficiently (in terms of
energy per unit angular momentum) such that they might be the important degrees
of freedom in the cores of neutron stars.Comment: 11 pages, accepted for publication in Physical Review
Two-Dimensional Helioseismic Power, Phase, and Coherence Spectra of {\it Solar Dynamics Observatory} Photospheric and Chromospheric Observables
While the {\it Helioseismic and Magnetic Imager} (HMI) onboard the {\it Solar
Dynamics Observatory} (SDO) provides Doppler velocity [], continuum
intensity [], and line-depth [] observations, each of which is
sensitive to the five-minute acoustic spectrum, the {\it Atmospheric Imaging
Array} (AIA) also observes at wavelengths -- specifically the 1600 and 1700
Angstrom bands -- that are partly formed in the upper photosphere and have good
sensitivity to acoustic modes. In this article we consider the characteristics
of the spatio--temporal Fourier spectra in AIA and HMI observables for a
15-degree region around NOAA Active Region 11072. We map the
spatio--temporal-power distribution for the different observables and the HMI
Line Core [], or Continuum minus Line Depth, and the phase and coherence
functions for selected observable pairs, as a function of position and
frequency. Five-minute oscillation power in all observables is suppressed in
the sunspot and also in plage areas. Above the acoustic cut-off frequency, the
behaviour is more complicated: power in HMI is still suppressed in the
presence of surface magnetic fields, while power in HMI and the AIA bands
is suppressed in areas of surface field but enhanced in an extended area around
the active region, and power in HMI is enhanced in a narrow zone around
strong-field concentrations and suppressed in a wider surrounding area. The
relative phase of the observables, and their cross-coherence functions, are
also altered around the active region. These effects may help us to understand
the interaction of waves and magnetic fields in the different layers of the
photosphere, and will need to be taken into account in multi-wavelength local
helioseismic analysis of active regions.Comment: 18 pages, 15 figures, to be published in Solar Physic
Multiwavelength Study on Solar and Interplanetary Origins of the Strongest Geomagnetic Storm of Solar Cycle 23
We study the solar sources of an intense geomagnetic storm of solar cycle 23
that occurred on 20 November 2003, based on ground- and space-based
multiwavelength observations. The coronal mass ejections (CMEs) responsible for
the above geomagnetic storm originated from the super-active region NOAA 10501.
We investigate the H-alpha observations of the flare events made with a 15 cm
solar tower telescope at ARIES, Nainital, India. The propagation
characteristics of the CMEs have been derived from the three-dimensional images
of the solar wind (i.e., density and speed) obtained from the interplanetary
scintillation data, supplemented with other ground- and space-based
measurements. The TRACE, SXI and H-alpha observations revealed two successive
ejections (of speeds ~350 and ~100 km/s), originating from the same filament
channel, which were associated with two high speed CMEs (~1223 and ~1660 km/s,
respectively). These two ejections generated propagating fast shock waves
(i.e., fast drifting type II radio bursts) in the corona. The interaction of
these CMEs along the Sun-Earth line has led to the severity of the storm.
According to our investigation, the interplanetary medium consisted of two
merging magnetic clouds (MCs) that preserved their identity during their
propagation. These magnetic clouds made the interplanetary magnetic field (IMF)
southward for a long time, which reconnected with the geomagnetic field,
resulting the super-storm (Dst_peak=-472 nT) on the Earth.Comment: 24 pages, 16 figures, Accepted for publication in Solar Physic
Three-body non-additive forces between spin-polarized alkali atoms
Three-body non-additive forces in systems of three spin-polarized alkali
atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio
calculations. The non-additive forces are found to be large, especially near
the equilateral equilibrium geometries. For Li, they increase the three-atom
potential well depth by a factor of 4 and reduce the equilibrium interatomic
distance by 0.9 A. The non-additive forces originate principally from chemical
bonding arising from sp mixing effects.Comment: 4 pages, 3 figures (in 5 files
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