84 research outputs found
Ab initio many-body calculations of the 3H(d,n)4He and 3He(d,p)4He fusion
We apply the ab initio no-core shell model/resonating group method approach
to calculate the cross sections of the 3H(d,n)4He and 3He(d,p)4He fusion
reactions. These are important reactions for the Big Bang nucleosynthesis and
the future of energy generation on Earth. Starting from a selected
similarity-transformed chiral nucleon-nucleon interaction that accurately
describes two-nucleon data, we performed many-body calculations that predict
the S-factor of both reactions. Virtual three-body breakup effects are obtained
by including excited pseudostates of the deuteron in the calculation. Our
results are in satisfactory agreement with experimental data and pave the way
for microscopic investigations of polarization and electron screening effects,
of the 3H(d,gamma)5He radiative capture and other reactions relevant to fusion
research.Comment: 4 pages, 3 figure
A new cross section measurement of reactions induced by 3He-particles on a carbon target
International audienceThe production of intense beams of light radioactive nuclei can be achieved at the SPIRAL2 facility using intense stable beams accelerated by the driver accelerator and impinging on light targets. The isotope 14O is identied to be of high interest for future experiments. The excitation function of the production reaction 12C(3He, n)14O was measured between 7 and 35 MeV. Results are compared with literature data. As an additional result, we report the rst cross-section measurement for the 12C(3He, +n)10C reaction. Based on this new result, the potential in-target 14O yield at SPIRAL2 was estimated: 2.4x1011 pps, for 1 mA of 3He at 35 MeV. This is a factor 140 higher than the in-target yield at SPIRAL1
A Comparison of Water Vapor Line Parameters for Modeling the Venus Deep Atmosphere
The discovery of the near infrared windows into the Venus deep atmosphere has
enabled the use of remote sensing techniques to study the composition of the
Venus atmosphere below the clouds. In particular, water vapor absorption lines
can be observed in a number of the near-infrared windows allowing measurement
of the H2O abundance at several different levels in the lower atmosphere.
Accurate determination of the abundance requires a good database of spectral
line parameters for the H2O absorption lines at the high temperatures (up to
~700 K) encountered in the Venus deep atmosphere. This paper presents a
comparison of a number of H2O line lists that have been, or that could
potentially be used, to analyze Venus deep atmosphere water abundances and
shows that there are substantial discrepancies between them. For example, the
early high-temperature list used by Meadows and Crisp (1996) had large
systematic errors in line intensities. When these are corrected for using the
more recent high-temperature BT2 list of Barber et al. (2006) their value of
45+/-10 ppm for the water vapor mixing ratio reduces to 27+/-6 ppm. The HITRAN
and GEISA lists used for most other studies of Venus are deficient in "hot"
lines that become important in the Venus deep atmosphere and also show evidence
of systematic errors in line intensities, particularly for the 8000 to 9500
cm-1 region that includes the 1.18 um window. Water vapor mixing ratios derived
from these lists may also be somewhat overestimated. The BT2 line list is
recommended as being the most complete and accurate current representation of
the H2O spectrum at Venus temperatures.Comment: 42 pages, 11 figures, Accepted by Icaru
Functionally heterogeneous human satellite cells identified by single cell RNA sequencing.
Although heterogeneity is recognized within the murine satellite cell pool, a comprehensive understanding of distinct subpopulations and their functional relevance in human satellite cells is lacking. We used a combination of single cell RNA sequencing and flow cytometry to identify, distinguish, and physically separate novel subpopulations of human PAX7+ satellite cells (Hu-MuSCs) from normal muscles. We found that, although relatively homogeneous compared to activated satellite cells and committed progenitors, the Hu-MuSC pool contains clusters of transcriptionally distinct cells with consistency across human individuals. New surface marker combinations were enriched in transcriptional subclusters, including a subpopulation of Hu-MuSCs marked by CXCR4/CD29/CD56/CAV1 (CAV1+). In vitro, CAV1+ Hu-MuSCs are morphologically distinct, and characterized by resistance to activation compared to CAV1- Hu-MuSCs. In vivo, CAV1+ Hu-MuSCs demonstrated increased engraftment after transplantation. Our findings provide a comprehensive transcriptional view of normal Hu-MuSCs and describe new heterogeneity, enabling separation of functionally distinct human satellite cell subpopulations
The rovibrational spectrum of BeH, MgH and CaH at high temperatures in the state: a theoretical study
Accurate line lists for three molecules, BeH, MgH and CaH, in their ground
electronic states are presented. These line lists are suitable for temperatures
relevant to exoplanetary atmospheres and cool stars (up to 2000K). A
combination of empirical and \textit{ab initio} methods is used. The
rovibrational energy levels of BeH, MgH and CaH are computed using the programs
Level and DPotFit in conjunction with `spectroscopic' potential energy curves
(PECs). The PEC of BeH is taken from the literature, while the PECs of CaH and
MgH are generated by fitting to the experimental transition energy levels. Both
spin-rotation interactions (except for BeH, for which it is negligible) and
non-adiabatic corrections are explicitly taken into account. Accurate line
intensities are generated using newly computed \textit{ab initio} dipole moment
curves for each molecule using high levels of theory. Full line lists of
rotation-vibration transitions for BeH, MgH, MgH, MgH
and CaH are made available in an electronic form as supplementary data
to this article and at \url{www.exomol.com}.Comment: MNRAS (in press
Asymptotic normalization coefficients from the (20)Ne((3)He, d)(21)Na reaction and astrophysical factor for (20)Ne(p,gamma)(21)Na
Journals published by the American Physical Society can be found at http://publish.aps.org/The (20)Ne(p,gamma)(21)Na reaction rate at stellar energies is dominated by capture to the ground state through the tail of a subthreshold resonance state at an excitation energy of 2425 keV in (21)Na. Both resonant and direct capture contribute to the reaction rate while direct captures to other bound states are negligible. The overall normalization of direct capture to the subthreshold state is determined by the asymptotic normalization coefficient (ANC). Simultaneously this ANC determines the proton partial width of the subthreshold resonance state. To determine the ANC, the (20)Ne((3)He,d)(21)Na proton transfer reaction has been measured, at an incident energy of 25.83 MeV. Angular distributions for proton transfer to the ground and first three excited states were measured, and ANCs were then extracted from comparison with distorted-wave Born approximation calculations. Using these ANCs, we calculated the astrophysical factor for (20)Ne(p,gamma)(21)Na. Our total astrophysical factor is S(0)=5900 +/- 1200 keV b. Our analysis confirms that only nonresonant and resonant captures through the subthreshold state are important
New astrophysical S factor for the (15)N(p,gamma)(16)O reaction via the asymptotic normalization coefficient (ANC) method
Journals published by the American Physical Society can be found at http://publish.aps.org/The (15)N(p,gamma)(16)O reaction provides a path from the CN cycle to the CNO bi-cycle and CNO tri-cycle. The measured astrophysical factor for this reaction is dominated by resonant capture through two strong J(pi) = 1(-) resonances at E(R) = 312 and 962 keV and direct capture to the ground state. Asymptotic normalization coefficients (ANCs) for the ground and seven excited states in (16)O were extracted from the comparison of experimental differential cross sections for the (15)N((3)He,d)(16)O reaction with distorted-wave Born approximation calculations. Using these ANCs and proton and alpha resonance widths determined from an R-matrix fit to the data from the (15)N(p,alpha)(12)C reaction, we carried out an R-matrix calculation to obtain the astrophysical factor for the (15)N(p,gamma)(16)O reaction. The results indicate that the direct capture contribution was previously overestimated. We find the astrophysical factor to be S(0) = 36.0 +/- 6.0 keV b, which is about a factor of 2 lower than the presently accepted value. We conclude that for every 2200 +/- 300 cycles of the main CN cycle one CN catalyst is lost due to this reaction
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