156 research outputs found
Observational confirmation of the Sun's CNO cycle
Gamma rays from a solar flare in Active Region 10039 on 23 July 2002 with the
RHESSI spacecraft spectrometer indicate that the CNO cycle occurs at the solar
surface, in electrical discharges along closed magnetic loops. At the two feet
of the loop, H ions are accelerated to energy levels that surpass Coulomb
barriers for the C-12[H-1, gamma]N-13 and N-14[H-1, gamma]O-15 reactions. First
x-rays appear along the discharge path. Next annihilation of positrons from
N-13 and O-15 [half-life = 10 m and 2 m] produce bright spots of 0.511 MeV
gammas at the loop feet. As C-13 increases from positron decay of N-13, the
C-13[He-4, n]O-16 reaction produces neutrons and then the 2.2 MeV emission line
appears from n-capture on H-1. These results suggest that the CNO cycle changed
the N-15/N-14 ratio in the solar wind and at the solar surface over geologic
time, and this ratio may contain an important historical record of climate
changes related to sunspot activity.Comment: 9 pages, 21 references, 2 figures show x-rays and gamma-rays from
nuclear reactions in a solar-flare-induced electrical discharge. Replaced to
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On the Cosmic Nuclear Cycle and the Similarity of Nuclei and Stars
Repulsive interactions between neutrons in compact stellar cores cause
luminosity and a steady outflow of hydrogen from stellar surfaces. Neutron
repulsion in more massive compact objects made by gravitational collapse
produces violent, energetic, cosmological events (quasars, gamma ray bursts,
and active galactic centers) that had been attributed to black holes before
neutron repulsion was recognized. Rather than evolving in one direction by
fusion, nuclear matter on the cosmological scale cycles between fusion,
gravitational collapse, and dissociation (including neutron-emission). This
cycle involves neither the production of matter in an initial Big Bang nor the
disappearance of matter into black holes. The similarity Bohr noted between
atomic and planetary structures extends to a similarity between nuclear and
stellar structures.Comment: 21 pages, 4 figure
How Social Enterprises Coordinate Cross-Sectoral Solutions for Informal Settlements: A Case Study of Terra Nova in Brazil
HonorsInternational StudiesUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/169405/1/mozinam.pd
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How does predicate invention affect human comprehensibility?
During the 1980s Michie defined Machine Learning in terms of two orthogonal axes of performance: predictive accuracy and comprehensibility of generated hypotheses. Since predictive accuracy was readily measurable and comprehensibility not so, later definitions in the 1990s, such as that of Mitchell, tended to use a one-dimensional approach to Machine Learning based solely on predictive accuracy, ultimately favouring statistical over symbolic Machine Learning approaches. In this paper we provide a definition of comprehensibility of hypotheses which can be estimated using human participant trials. We present the results of experiments testing human comprehensibility of logic programs learned with and without predicate invention. Results indicate that comprehensibility is affected not only by the complexity of the presented program but also by the existence of anonymous predicate symbols
Stability of Diethyl Carbonate in the Presence of Acidic and Basic Solvents
Reducing carbon dioxide (CO2) emissions is an inevitable measure for fighting anthropogenic climate change. Carbon Capture and Utilization (CCU) technologies are gaining rising attention as an additional contributor to reaching the Paris Agreement goals. Giving CO2 a value as a feedstock to be refined into chemicals to be used in industry is a crucial aspect of making these technologies interesting for vast industrial sectors. The synthesis of diethyl carbonate (DEC) is recognized as a promising prospect for the successful implementation of CCU. DEC is considered a fully biodegradable, low-toxic solvent, which can be synthesized from CO2 and ethanol in the presence of a catalyst. DEC may be a non-toxic alternative to other solvents such as toluene or methyl isobutyl ketone (MIBK).
The optimization of DEC synthesis is one aspect that is under investigation today. For the exploration of DEC's applicability, an extensive amount of data is beneficial. Many applications of solvents involve the presence of acids and bases. Hence, an interest in DEC in various environments is reasonable. The decomposition of DEC after contact with water, different acids and bases at room temperature, and the boiling point was determined experimentally to characterize chemical stability. Further, the influence of sodium chloride and a cerium-based catalyst used in DEC synthesis was investigated
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