338 research outputs found
The strength of nuclear shell effects at N=126 in the r-process region
We have investigated nuclear shell effects across the magic number N=126 in
the region of the r-process path. Microscopic calculations have been performed
using the relativistic Hartree-Bogoliubov approach within the framework of the
RMF theory for isotopic chains of rare-earth nuclei in the r-process region.
The Lagrangian model NL-SV1 with the inclusion of the vector self-coupling of
omega meson has been employed. The RMF results show that the shell effects at
N=126 remain strong and exhibit only a slight reduction in the strength in
going from the r-process path to the neutron drip line. This is in striking
contrast to a systematic weakening of the shell effects at N=82 in the
r-process region predicted earlier in the similar approach. In comparison the
shell effects with microscopic-macroscopic mass formulae show a near constancy
of shell gaps leading to strong shell effects in the region of r-process path
to the drip line. A recent analysis of solar-system r-process abundances in a
prompt supernova explosion model using various mass formulae including the
recently introduced mass tables based upon HFB approach shows that whilst mass
formulae with weak shell effects at N=126 give rise to a spread and an
overproduction of nuclides near the third abundance peak at A~190, mass tables
with droplet models showing stronger shell effects are able to reproduce the
abundance features near the third peak appropriately. In comparison, several
analyses of the second r-process peak at A~130 have required weakened shell
effects at N=82. Our predictions in the RMF theory with NL-SV1, which exhibit
weaker shell effects at N=82 and stronger one at N=126 in the r-process region,
support the conjecture that a different nature of the shell effects at the
magic numbers may be at play in r-process nucleosynthesis of heavy nuclei.Comment: 14 pages, 8 figures; submitted to Physical Review C. Part of this
work was presented at Nuclear Physics in Astrophysics II, 20th International
Nuclear Physics Divisional Conference of the European Physical Society, at
Debrecen, Hungary, May 16-20, 200
Fission Cycling in a Supernova r-process
Recent halo star abundance observations exhibit an important feature of
consequence to the r-process: the presence of a main r-process between the
second and third peaks which is consistent among halo stars. We explore fission
cycling and steady-beta flow as the driving mechanisms behind this feature. The
presence of fission cycling during the r-process can account for
nucleosynthesis yields between the second and third peaks, whereas the presence
of steady-beta flow can account for consistent r-process patterns, robust under
small variations in astrophysical conditions. We employ the neutrino-driven
wind of the core-collapse supernova to examine fission cycling and steady-beta
flow in the r-process. As the traditional neutrino-driven wind model does not
produce the required very neutron-rich conditions for these mechanisms, we
examine changes to the neutrino physics necessary for fission cycling to occur
in the neutrino-driven wind environment, and we explore under what conditions
steady-beta flow is obtained.Comment: 9 pages, 8 figure
Application of the RMF mass model to the r-process and the influence of mass uncertainties
A new mass table calculated by the relativistic mean field approach with the
state-dependent BCS method for the pairing correlation is applied for the first
time to study r-process nucleosynthesis. The solar r-process abundance is well
reproduced within a waiting-point approximation approach. Using an exponential
fitting procedure to find the required astrophysical conditions, the influence
of mass uncertainty is investigated. R-process calculations using the FRDM,
ETFSI-Q and HFB-13 mass tables have been used for that purpose. It is found
that the nuclear physical uncertainty can significantly influence the deduced
astrophysical conditions for the r-process site. In addition, the influence of
the shell closure and shape transition have been examined in detail in the
r-process simulations.Comment: to be published in Phys. Rev. C, 22 pages, 9 figure
Molecular Characterization of \u3ci\u3eCitrus tatter leaf virus\u3c/i\u3e Historically Associated with Meyer Lemon Trees: Complete Genome Sequence and Development of Biologically Active In Vitro Transcripts
Citrus tatter leaf virus isolated from Meyer lemon trees (CTLV-ML) from California and Florida induces bud union incompatibility of citrus trees grafted on the widely used trifoliate and trifoliate hybrid rootstocks. The complete genome sequence of CTLV-ML was determined to be 6,495 nucleotides (nts), with two overlapping open reading frames (ORFs) and a poly (A) tail at the 3′ end. The genome organization is similar to other capilloviruses, with ORF1 (nts 37 to 6,354) encoding a putative 242-kDa polyprotein which contains replication-associated domains plus a coat protein (CP), and ORF2 (nts 4,788 to 5,750), which is located within ORF1 in a different reading frame and encodes a putative movement protein. Although the proteins encoded by CTLV-ML possesses 84 to 96% amino acid sequence identity with strains of Apple stem grooving virus (ASGV), we observed two strikingly different regions in ORF1: variable region I (amino acids 532 to 570) and variable region II (amino acids 1,583 to 1,868), with only 15 to 18 and 56 to 62% identities, respectively, with the corresponding regions of ASGV strains. Conditions for a herbaceous systemic assay host were optimized in which the wildtype virus induced systemic infection in Phaseolus vulgaris cv. Light Red Kidney (LRK) bean plants at 19 or 22°C but not at higher temperatures. In vitro transcripts generated from full-length cDNA clones induced systemic symptoms on LRK bean plants similar to that of the wild-type virus. Replication of the recombinant virus was confirmed by hybridization of a 5′ positive-stranded RNA-specific probe to a genome-sized RNA and by reverse-transcription polymerase chain reaction
Characterization of the 5′- and 3′-Terminal Subgenomic RNAs Produced by a Capillovirus: Evidence for a CP Subgenomic RNA
The members of Capillovirus genus encode two overlapping open reading frames (ORFs): ORF1 encodes a large polyprotein containing the replication-associated proteins plus a coat protein (CP), and ORF2 encodes a movement protein (MP), located within ORF1 in a different reading frame. Organization of the CP sequence as part of the replicase ORF is unusual in capilloviruses. In this study, we examined the capillovirus genome expression strategy by characterizing viral RNAs produced by Citrus tatter leaf virus (CTLV), isolate ML, a Capillovirus. CTLV-ML produced a genome-length RNA of ∼6.5-kb and two 3′-terminal sgRNAs in infected tissue that contain the MP and CP coding sequences (3′-sgRNA1), and the CP coding sequence (3′-sgRNA2), respectively. Both 3′-sgRNAs initiate at a conserved octanucleotide (UUGAAAGA), and are 1826 (3′-sgRNA1) and 869 (3′-sgRNA2) nts with 119 and 15 nt leader sequences, respectively, suggesting that these two 3′- sgRNAs could serve to express the MP and CP. Additionally, accumulation of two 5′-terminal sgRNAs of 5586 (5′-sgRNA1) and 4625 (5′-sgRNA2) nts was observed, and their 3′-termini mapped to 38–44 nts upstream of the transcription start sites of 3′-sgRNAs. The presence of a separate 3′-sgRNA corresponding to the CP coding sequence and its cognate 5′-terminal sgRNA (5′-sgRNA1) suggests that CTLV-ML produces a dedicated sg mRNA for the expression of its CP
Neutrino-induced fission of neutron-rich nuclei
We calculate neutrino-induced fission cross sections for selected nuclei with
Z=84-92. We show that these reactions populate the daughter nucleus at
excitation energies where shell effects are significantly washed out,
effectively reducing the fission barrier. If the r-process occurs in the
presence of a strong neutrino fluence, and electron neutrino average energies
are sufficiently high, perhaps as a result of matter-enhanced neutrino flavor
transformation, then neutrino-induced fission could lead to significant
alteration in the r-process flow in slow outflow scenarios.Comment: 4 pages, three figure
Phase shift experiments identifying Kramers doublets in a chaotic superconducting microwave billiard of threefold symmetry
The spectral properties of a two-dimensional microwave billiard showing
threefold symmetry have been studied with a new experimental technique. This
method is based on the behavior of the eigenmodes under variation of a phase
shift between two input channels, which strongly depends on the symmetries of
the eigenfunctions. Thereby a complete set of 108 Kramers doublets has been
identified by a simple and purely experimental method. This set clearly shows
Gaussian unitary ensemble statistics, although the system is time-reversal
invariant.Comment: RevTex 4, 5 figure
Confinement in the Deconfined Phase: A numerical study with a cluster algorithm
We have previously found analytically a very unusual and unexpected form of
confinement in SU(3) Yang-Mills theory. This confinement occurs in the
deconfined phase of the theory. The free energy of a single static test quark
diverges, even though it is contained in deconfined bulk phase and there is no
QCD string present. This phenomenon occurs in cylindrical volumes with a
certain choice of spatial boundary conditions. We examine numerically an
effective model for the Yang-Mills theory and, using a cluster algorithm, we
observe this unusual confinement. We also find a new way to determine the
interface tension of domain walls separating distinct bulk phases.Comment: LaTex, 14 pages, 4 figure
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