10,141 research outputs found
Nucleon-Nucleon Scattering From Fully-Dynamical Lattice QCD
We present results of the first fully-dynamical lattice QCD determination of
nucleon-nucleon scattering lengths in the 1S0 channel and 3S1-3D1 coupled
channels. The calculations are performed with domain-wall valence quarks on the
MILC staggered configurations with lattice spacing of b=0.125 fm in the
isospin-symmetric limit, and in the absence of electromagnetic interactions.Comment: 4 pages, 4 figure
A hydrogen energy carrier. Volume 2: Systems analysis
A systems analysis of hydrogen as an energy carrier in the United States indicated that it is feasible to use hydrogen in all energy use areas, except some types of transportation. These use areas are industrial, residential and commercial, and electric power generation. Saturation concept and conservation concept forecasts of future total energy demands were made. Projected costs of producing hydrogen from coal or from nuclear heat combined with thermochemical decomposition of water are in the range 1.50 per million Btu of hydrogen produced. Other methods are estimated to be more costly. The use of hydrogen as a fuel will require the development of large-scale transmission and storage systems. A pipeline system similar to the existing natural gas pipeline system appears practical, if design factors are included to avoid hydrogen environment embrittlement of pipeline metals. Conclusions from the examination of the safety, legal, environmental, economic, political and societal aspects of hydrogen fuel are that a hydrogen energy carrier system would be compatible with American values and the existing energy system
A hydrogen energy carrier. Volume 1: Summary
The production, technology, transportation, and implementation of hydrogen into the energy system are discussed along with the fossil fuel cycle, hydrogen fuel cycle, and the demands for energy. The cost of hydrogen production by coal gasification; electrolysis by nuclear energy, and solar energy are presented. The legal aspects of a hydrogen economy are also discussed
High temporal frequency measurements of greenhouse gas emissions from soils
Carbon dioxide (CO<sub>2</sub>), methane (CH<sub>4</sub>), and nitrous oxide (N<sub>2</sub>O)
are the most important anthropogenic greenhouse gases (GHGs). Variation in soil
moisture can be very dynamic, and it is one of the dominant factors
controlling the net exchange of these three GHGs. Although
technologies for high-frequency, precise measurements of CO<sub>2</sub> have been
available for years, methods for measuring soil fluxes of CH<sub>4</sub> and
N<sub>2</sub>O at high temporal frequency have been hampered by lack of appropriate
technology for in situ real-time measurements. A previously developed
automated chamber system for measuring CO<sub>2</sub> flux from soils was
configured to run in line with a new quantum cascade laser (QCLAS) instrument
that measures N<sub>2</sub>O and CH<sub>4</sub>. Here we present data from a forested
wetland in Maine and an agricultural field in North Dakota, which provided
examples of both net uptake and production for N<sub>2</sub>O and CH<sub>4</sub>. The
objective was to provide a range of conditions in which to run the new system
and to compare results to a traditional manual static-chamber method.
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The high-precision and more-than-10-times-lower minimum detectable flux of
the QCLAS system, compared to the manual system, provided confidence in
measurements of small N<sub>2</sub>O uptake in the forested wetland. At the
agricultural field, the greatest difference between the automated and manual
sampling systems came from the effect of the relatively infrequent manual
sampling of the high spatial variation, or "hot spots", in GHG fluxes.
Hot spots greatly influenced the seasonal estimates, particularly for
N<sub>2</sub>O, over one 74-day alfalfa crop cycle. The high temporal frequency of
the automated system clearly characterized the transient response of all
three GHGs to precipitation and demonstrated a clear diel pattern related to
temperature for GHGs. A combination of high-frequency automated and
spatially distributed chambers would be ideal for characterizing hot
spots and "hot moments" of GHG fluxes
GHRS and ORFEUS-II Observations of the Highly Ionized Interstellar Medium Toward ESO141-055
We present Goddard High Resolution Spectrograph and ORFEUS-II measurements of
Si IV, CIV, N V, and O VI absorption in the interstellar medium of the Galactic
disk and halo toward the nucleus of the Seyfert galaxy ESO141-055. The high
ionization absorption is strong, with line strengths consistent with the
spectral signature expected for hot (log T = 5-6) collisionally ionized gas in
either a ``Galactic fountain'' or an inhomogeneous medium containing a mixture
of conductive interfaces and turbulent mixing layers. The total O VI column
density of log N ~ 15 suggests that the scale height of O VI is large (>3 kpc)
in this direction. Comparison of the high ion column densities with
measurements for other sight lines indicates that the highly ionized gas
distribution is patchy. The amount of O VI perpendicular to the Galactic plane
varies by at least a factor of ~4 among the complete halo sight lines thus far
studied. In addition to the high ion absorption, lines of low ionization
species are also present in the spectra. With the possible exception of Ar I,
which may have a lower than expected abundance resulting from partial
photoionization of gas along the sight line, the absorption strengths are
typical of those expected for the warm, neutral interstellar medium. The sight
line intercepts a cold molecular cloud with log N(H2) ~ 19. The cloud has an
identifiable counterpart in IRAS 100-micron emission maps of this region of the
sky. We detect a Ly-alpha absorber associated with ESO141-055 at z = 0.03492.
This study presents an enticing glimpse into the interstellar and intergalactic
absorption patterns that will be observed at high spectral resolution by the
Far Ultraviolet Spectroscopic Explorer.Comment: 24 pages + 8 figures, uses aaspp4.sty. Accepted for publication in
Ap
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