723 research outputs found
Stationary states of fermions in a sign potential with a mixed vector-scalar coupling
The scattering of a fermion in the background of a sign potential is
considered with a general mixing of vector and scalar Lorentz structures with
the scalar coupling stronger than or equal to the vector coupling under the
Sturm-Liouville perspective. When the vector coupling and the scalar coupling
have different magnitudes, an isolated solution shows that the fermion under a
strong potential can be trapped in a highly localized region without
manifestation of Klein's paradox. It is also shown that the lonely bound-state
solution disappears asymptotically as one approaches the conditions for the
realization of spin and pseudospin symmetries.Comment: 4 figure
Scattering and bound states of fermions in a mixed vector-scalar smooth step potential
The scattering of a fermion in the background of a smooth step potential is
considered with a general mixing of vector and scalar Lorentz structures with
the scalar coupling stronger than or equal to the vector coupling.
Charge-conjugation and chiral-conjugation transformations are discussed and it
is shown that a finite set of intrinsically relativistic bound-state solutions
appears as poles of the transmission amplitude. It is also shown that those
bound solutions disappear asymptotically as one approaches the conditions for
the realization of the so-called spin and pseudospin symmetries in a
four-dimensional space-time.Comment: 5 figures. arXiv admin note: substantial text overlap with
arXiv:1310.847
The developmental stage of inactivation of rye origin rRNA genes in the embryo and endosperm of wheat x rye F1 hybrids
To identify the developmental stage during which the
preferential inactivation of rRNA genes from the rye
parent occurs in wheat x rye hybrids, nucleolar activity
was evaluated in the embryo and endosperm of
developing seeds of the hybrids. The hybrids were
obtained from crosses of euploid and aneuploid lines
of hexaploid wheat, Triticum aestivum cv. Chinese
Spring, with rye, Secale cereale cv. Centeio do
Alto. The number of nucleolar organizing regions
(NORs) and nucleoli present in the embryo and endosperm
cells of wheat, and wheat × rye F1 hybrids, at
different times after fertilization was scored by silver
staining. The inactivation of rDNA of rye origin in F1
hybrids occurs simultaneously in the embryo and in
the endosperm between 4 and 5 days after fertilization,
when these have been through six and 10 cell cycles
respectively. We conclude that the genomic interactions
leading to the inactivation of the rye origin rDNA
is a time-dependent process, related to the developmental
stage and independent of the number of cell
cycles (DNA replication rounds) they have been
through
Levantamento das etapas do processo de rastreabilidade bovina em propriedades dos municípios de Dom Pedrito e Bagé.
CONGREGA 2012
Reprogramming of rye rDNA in triticale during microsporogenesis
To test the hypothesis that interspecific genomic and
chromosome interactions leading to nucleolar dominance
could be reprogrammed in meiosis, we compared
the expression of distinct nucleolar
organizing region (NOR) loci in hexaploid triticale root
tip meristematic cells, pollen mother cells and young
pollen grains. Interphase and metaphase cells were
silver stained to quantify nucleoli and active NOR loci
respectively. A marked difference in the ribosomal
RNA gene activity of each locus was observed when
different types of cells were compared: in somatic and
pollen mother cells, rRNA gene activity was mainly
restricted to major wheat NORs (1B and 6B) with only
a small contribution from rye NORs (1R). In contrast, in
young pollen grains, all NORs present, including the
1R NORs, were consistently active. The expression of
all NORs just after meiosis is considered to be a consequence
of meiotic reprogramming of rye origin
rDNA. Gene reprogramming mediated by the resetting
of methylation patterns established early in embryogenesis
is suggested to be responsible for the differential
expression of the NORs of rye origin in distinct
developmental stages of triticale
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