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Tensor Forces and the Ground-State Structure of Nuclei
Two-nucleon momentum distributions are calculated for the ground states of
nuclei with mass number , using variational Monte Carlo wave functions
derived from a realistic Hamiltonian with two- and three-nucleon potentials.
The momentum distribution of pairs is found to be much larger than that of
pairs for values of the relative momentum in the range (300--600) MeV/c
and vanishing total momentum. This order of magnitude difference is seen in all
nuclei considered and has a universal character originating from the tensor
components present in any realistic nucleon-nucleon potential. The correlations
induced by the tensor force strongly influence the structure of pairs,
which are predominantly in deuteron-like states, while they are ineffective for
pairs, which are mostly in S states. These features should be
easily observable in two-nucleon knock-out processes, such as and .Comment: 4 pages including 3 figure
Dependence of two-nucleon momentum densities on total pair momentum
Two-nucleon momentum distributions are calculated for the ground states of
3He and 4He as a function of the nucleons' relative and total momenta. We use
variational Monte Carlo wave functions derived from a realistic Hamiltonian
with two- and three-nucleon potentials. The momentum distribution of pp pairs
is found to be much smaller than that of pn pairs for values of the relative
momentum in the range (300--500) MeV/c and vanishing total momentum. However,
as the total momentum increases to 400 MeV/c, the ratio of pp to pn pairs in
this relative momentum range grows and approaches the limit 1/2 for 3He and 1/4
for 4He, corresponding to the ratio of pp to pn pairs in these nuclei. This
behavior should be easily observable in two-nucleon knock-out processes, such
as A(e,e'pN).Comment: 3 pages, 3 figure
Quantum Monte Carlo calculations of excited states in A = 6--8 nuclei
A variational Monte Carlo method is used to generate sets of orthogonal trial
functions, Psi_T(J^pi,T), for given quantum numbers in various light p-shell
nuclei. These Psi_T are then used as input to Green's function Monte Carlo
calculations of first, second, and higher excited (J^pi,T) states. Realistic
two- and three-nucleon interactions are used. We find that if the physical
excited state is reasonably narrow, the GFMC energy converges to a stable
result. With the combined Argonne v_18 two-nucleon and Illinois-2 three-nucleon
interactions, the results for many second and higher states in A = 6--8 nuclei
are close to the experimental values.Comment: Revised version with minor changes as accepted by Phys. Rev. C. 11
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Increased dietary zinc oxide changes the bacterial core and enterobacterial composition in the ileum of piglets
This study was conducted to investigate the effects of increased dietary ZnO
on the bacterial core and enterobacterial composition in the small intestine
of piglets that were fed diets containing a total of 124 or 3,042 mg of Zn per
kilogram of diet, respectively. Zinc was supplemented to the basal diet as
ZnO. Bacterial 16S rRNA genes of ileal DNA extracts were PCR-amplified with 2
bar-coded primer sets and sequenced by 454 pyrosequencing. The bacterial core
species were calculated from the relative abundances of reads present in 5 of
6 samples per group and at a minimum of 5 sequences per sample. The reference
database SILVA was used to assign sequence reads at an alignment minimum of
200 bases and 100% identity. Lactic acid bacteria dominated the bacterial
core, but showed diverse responses to dietary ZnO. Of the dominant
Lactobacillus spp., Lactobacillus reuteri was reduced due to increased dietary
ZnO (44.7 vs. 17.9%; P=0.042), but L. amylovorus was not influenced. However,
the changes of relative abundances of other lactic acid bacteria were more
noteworthy; Weissella cibaria (10.7 vs. 23.0%; P=0.006), W. confusa (10.0 vs.
22.4%; P=0.037), Leuconostoc citreum (6.5 vs. 14.8%; P=0.009), Streptococcus
equinus (0.14 vs. 1.0%; P=0.044), and S. lutetiensis (0.01 vs. 0.11%; P=0.016)
increased in relative abundance. Nonlactic acid bacteria that were influenced
by increased dietary ZnO included the strict anaerobic species, Sarcina
ventriculi, which showed a strong numerical decrease in relative abundance
(14.6 vs. 5.1%). Species of the Enterobacteriaceae increased their relative
abundance, as well as species diversity, in the high dietary ZnO experimental
group. Bacterial diversity indices were increased due to increased dietary ZnO
(P < 0.05), which was traced back to the increase of sequences from
subdominant species. Increased dietary ZnO led to an increase of less
prominent species and, thus, had a major impact on the bacterial composition
and diversity in piglets. This effect may help to stabilize the intestinal
microbiota in the sensitive postweaning period
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